How grim can it be?

Maurice Sendak is an American Jew whose relatives died in the Holocaust. He is also an artist and storyteller, well aware of children's love of shock, and unable to suppress his own glee and optimism in the face of horror. The playwright Tony Kushner, who is collaborating with him in a book that embraces all these elements, celebrates an old friend

Maurice Sendak and I have been good friends for a decade. His early books were a central part of my first experience of literature, as they were for many Americans of my generation. Sendak books are still central to American children, though not necessarily the same Sendak books. I grew too old for picture books - or at least I believed I had to pretend I had - a year or two before Where The Wild Things Are was published in 1963. In truth, I never managed to move far from picture books.

Before we became friends, I'd encountered Maurice, briefly, in 1979. I was working at B Dalton's Books on Fifth Avenue, my first crummy job after graduation. Maurice came to sign copies of his books. Even though I could get an employee's tiny discount, with my tiny, tiny paycheque it was hard to scrounge up the money to buy a copy of the slipcased two volumes of The Juniper Tree, expensive at $25, but scrounge it I did, and the nerve as well to ask Maurice to sign it. He signed and drew a little cat; he smiled in a friendly fashion, and that was that.

He was unfailingly polite to the long line of people who'd come to the signing. Maurice is rather courtly in his dealings with other people, except when provoked, and even then he merely bares his teeth and growls, behaviour he may have learned from generations of canine companions. His desire for solitude notwithstanding, he is not a hermit. He is in fact gregarious, observant and curious about people, as I think most artists are inclined to be.

The affectionate and sociable impulse in Maurice, however, is countermanded by a self-protective privacy, an inward gazing that has as one of its sources a childhood of illness in an atmosphere of pressurised familial closeness. Immigrants' child, Brooklyn child: such children were loved while at the same time inculcated with ghetto-bred tribal fearfulness and insecurity. Maurice is a child of the Great Depression and of Jewish Depression, if I may generalise. Jewish Depression is that inherited awareness of the arduousness of knowing God, the arduousness of knowing anything, an acute awareness of the struggle to know, the struggle against not knowing; and it is that enduring sense of displacement, yearning for and not securely possessing a home. Maurice's is a Yiddische kopf, a large, brooding, circumspect and contemplative mind, darkened by both fatalism and faith.

Last winter, I learned he never uses his fireplace. I told him, "I use mine every chance I get!" He replied, "You, you're an emancipated Jew, you don't know fire will kill you! I will never unlearn that!"

Being a self, alone, committed to oneness, whether through predilection or through a conviction of the necessity of the condition of aloneness, is a part of what Harold Bloom has termed Jewish interiority. Children's literature may reflect the pleasant, booming confusion of the world in a thousand ways; it may describe earthly pleasures; it may be the most profoundly materialist (in the philosophical sense) and the most thoroughly sensual literature. But it is the product of a solitary, and a lonely, pursuit. For the great adult creators of children's books, the work at hand is a reclamation, through the difficult exploration of feelings most people have forgotten, of the past.

Maurice is not an observant Jew, but he is deeply Jewish. Like most Jews, he is shadowed always by the Holocaust. Relatives of his who didn't make it to America died in the camps. In much of his work, obeisance is made to these ghosts. But Sendak is also echt an American Jew. As has been immemorially true of Jews, but especially in countries where Jews have not been subject to oppression and mass murder, American Jews have been hungry and brilliant absorbers, assimilators, students of culture, both American and cosmopolitan. Maurice is representative of his generation in this regard, the autodidact Jewish kid in the public library. He didn't attend college; hungry to succeed, he began his career as an artist immediately after high school. In spite of this, he's encyclopedically conversant with antecedents in poetry, fiction, painting and music.

Knowledge intoxicates Maurice, it's an aphrodisiac. It seems likely to me that his partner of many years, Dr Eugene Glynn, a psychoanalyst, a man of vast learning as well as fierce opinions, has helped guide him in his study. Maurice has over the years befriended writers, artists and dancers, including Randall Jarrell, Grace Paley, Coleman Dowell, Philip Roth, Twyla Tharp, Jules Feiffer and Marianne Moore. He is instantly alert at the mention of a new book, a new idea.

Maurice's love of people is great and wide, as is his interest in their doings - heroic, monstrous, and everything in between. His need for their company is more circumscribed. He will invoke one of his favourite poets, Emily Dickinson, tutelary divinity of reclusiveness. "What I learned from her," he told me, "is, 'Don't open the door, don't let them in!' " Then he enacts an imagined domestic drama from the Dickinson home in Amherst, doing all the characters: "'Emily, Emily, you promised you'd come for a snow ride with us! What are you doing sulking upstairs?' 'Don't listen, don't care, don't let them in!' And she stayed upstairs. She didn't listen to them. She kept the world OUT," he concludes, full of admiration.

Yet sociable Mozart and Keats are heroes as well. Sendak in hiding attracts an ever-expanding army of friends. I'm forever meeting people who know him, who have visited him, who have worked or corresponded with him.

The object of such devotion is frequently a source of concern among the devoted. Maurice's is a bumpy life, with a lion's share of physical difficulty. His tough, sturdy-seeming body, beset since his early coronary - since early childhood, perhaps - has rarely had a moment's peace, and at times threatens to fall to pieces; he marshals himself back to health and to the drawing board by dint of will and with the help of medication. Septuagenarians confront, day in and day out, the loss of loved ones. This is hard, especially for a man of more than ordinary loyalty and ferocious affection. In the ferocity of his affection you come to understand Maurice's affinity for children; in his loyalty you come to understand his spiritual kinship with dogs.

Maurice is a champion lamenter, which is different from saying he's a kvetch . Kvetching is annoying. Lamentation is a kind of poetic indictment; it is a sorrow and a joy to hear. Maurice's lamentation has a recognisable Jewish cadence, spiced with Anglo-Saxon invective. When his wrath (there's no other word for it) is aroused, his vituperation is alliterative and bloody and guttural and as scorching as dragon's breath. It's quite shocking when you first hear America's greatest author of children's books raging like a mad Danish sailor, raging like Nixon, or rather like Nixon might have raged had he possessed Maurice's musicality and well-fed poet's ear.

The shock is intended. Shock, after all, is a way to collect devotees. If you want someone to be your friend for life, you must at some point shock them. How else to fascinate other than by being unpredictable, how else to raze dividing walls other than by blowing a barbarous yawp or two on your brass or goat-horn trumpet?

Maurice delves in a field in which shock, scandal, even the censor's wrath, was, if anything, too easily come by, children's literature (at least until very recently) being in this regard rather like Hawthorne's New England or some small town in the 1950s or like a Stalin-era eastern European country. The best children's authors and illustrators have always shocked; the temptation is irresistible when the interdiction is so formidable and unreasonable. And good children's authors, like any good authors, must know their audiences. Children like being shocked. To the dark gothic forest breezes blowing icily through the Brothers Grimm can be attributed, perhaps more than to any other quality, their tales' immortal appeal. Consider Hans Christian Andersen's lavishly suffering children, his predilection for tortured feet - those little girls treading on loaves and knife blades. Think of Lewis Carroll, of Tenniel's rat-fanged Jabberwock; think of the heartbreak and emotional overload you attempted to incorporate over EB White's poor dead Charlotte or Bambi's murdered mother.

Nowadays, children's authors often resort to vulgar, unimaginative means for providing the joy of transgression. Offering an abundance of ordure, symphonies of bodily eructation, reading for all the world as if children had written them, sowing in consequence nothing more than seeds of regressive incapacity, of slacker-slobbism, the books these panderers write and illustrate are mere preparatory manuals for future citizenship in the Global Kakatopian Empire. The best children's literature expresses the hope (melancholic though it is) that children won't stay children for ever.

Maurice, among the best of the best, shocks deeply, touching on the mortal, the insupportably sad or unjust, even on the carnal, on the primal rather than the merely primitive. He pitches children, including aged children, out of the familiar and into mystery, and then into understanding, wisdom even. He pitches children through fantasy into human adulthood, that rare, hard-won and, let's face it, tragic condition.

There used to be a handsome reporter on one of the New York television newscasts who always looked badly startled, no matter what he was talking about, his face an attractive rictus of blanched alarm. A friend of mine, a psychoanalytic grad student, watching this guy, remarked, "He looks like he's never recovered from his primal scene." I decided at that instant to read any expression of perpetual surprise as evidence of unmended early developmental trauma. I suspect it in Maurice. Don't get me wrong - he has a beautiful face, with wide, pale, almond-shaped eyes. After a lifetime of looking, he wears glasses with thick lenses - maybe they've always been thick, but I choose to think of the thickness as recent, his spectacles a badge of suffering for his art. These magnify his eyes, in which some wondering wildness resides, tough and also furtive. They're startled and startling, his eyes, like saltwater deep-sea pressure-resistant fish, at swim behind dense aquarium glass. They are capped by eyebrows that are more often than not semicircles of astonishment. These lower only when he's faced with a lovely person or a lovely painting, when listening to great music, when moved by some act of kindness, when feeling sympathy or grief, when he's disarmed. Otherwise they arch, 75 years of muscular contraction holding them effortlessly, exclamatorily high.

While I was still an undergraduate, probably in 1975, I went to an exhibition of illustrated books at the New York Public Library. I purchased a 1972 Library of Congress pamphlet entitled Questions To An Artist Who Is Also An Author: A Conversation Between Maurice Sendak And Virginia Haviland. One moment in the exchange has always stayed with me, which according to my memory went something like this:

Miss Haviland: One critic has asked why you changed from the "fine engraved style" of Higglety Pigglety Pop! back to what this person calls the "fat style" of your earlier work? Mr Sendak: Umm, "fat style". Well...

He went on to say, as one would, that it's important for an artist to avoid fetishising and fossilising his or her "style", that different subject matter demands differing graphic approaches, "a fine style, a fat style, a fairly slim style, and an extremely stout style". But what sank in my soul was, "Umm, 'fat style'." Why?

One reason, I suppose, is that I heard in his remark that Maurice was receiving a blow and absorbing it. One would wish that a man of such accomplishment had a thicker skin, but in the past 10 years or so I've met a number of eminent artists, and not one of them, no matter how venerated, is genuinely indifferent to the value of their stock, if you will.

"Um" is a swallowing sound. The speaker makes it when, aware or not, he or she has words to say, a response to make, which must not be spoken, which must be gulped down instead. "Umm", on the other hand, might start out as simple ingestion - the insult is being incorporated. But that rolling "mm" suggests other things: contemplation - the remark is being weighed; degustation - the insult is being savoured. It might, as it slips from the ululatory to the guttural, be the beginning of a growl - "Ummmmm". Watch it!

Whatever it means, I suspect the "umm" is the reason I have always remembered the exchange with Miss Haviland. I'm not the first person writing about Maurice to cite the phoneme he ummed that day in 1972. "Umm" is a Sendakian sound. He has always reckoned with the power of gabble, of the ur-syllables that make up words. At the time of the interview, In The Night Kitchen had just been published (and was, in fact, the book that the unnamed critic had declared rendered in a "fat style"), with the "bump" and the "clump" that send Mickey off on his flight. Higglety Pigglety Pop! begins with nonsense words and ends with a play, the denouement of which reads as follows:

"Pop!"
"Stop!"
"Clop!"
"Chop!"
THE END

Samuel Beckett couldn't have put it more concisely.

Nothing gives kids more pleasure than laughing at baby gibberish. It's a way of marking and securing their great accomplishment, their accession into the world of language; they are horribly delighted to recall the gabble it took such hard work to escape. And they miss terribly the freedom simply to make up words instead of submitting wordless feeling and impulse to that tyrant, the dictionary. The best people refuse to submit. Mozart, in a letter to his sister, coins the word "Schlumba!" and many others you won't find in a Langenscheidt's. Edward Lear's Mr and Mrs Discobbolos exclaim, in an access of anguish or delight, "Oh W X Y Z!" Lewis Carroll chortled, "Oh frabjous day! Callooh! Callay!" To which colloquium Maurice Sendak and Ruth Krauss [his frequent collaborator] have added their two bits: "Boodlyboodlyboodly..."

Recently Maurice has been working on opera designs for Brundibar, by Hans Krasa. Brundibar, Czech for bumblebee, tells the story of two small children, Pepicek and Aninku, whose mother has fallen ill; the brother and sister travel to a nearby city to bring back milk to make her well. Upon arriving, the children realise that they need money, and their attempt to earn some by singing in the town square is thwarted by the villain of the opera, Brundibar, a teenage hurdy-gurdy player and a bully. Frightened, the two kids hide in an alley; they are rescued by a friendly sparrow, cat and dog who, along with 300 schoolkids enlisted for the purpose, help Aninku and Pepicek drive the bully away. The kids sing a beautiful choral number, and consequently get plenty of cash from an appreciative audience of grown-ups to buy milk for their mother, who drinks the milk, or mleko, as it is called in Czech (say it out loud and you will realise that it's a much better word than its English equivalent), and is restored to health.

It's a sweet tale, but it has a tragic history. In 1938, the Czech Ministry of Education and Culture sponsored a competition for a children's opera. I haven't been able to find out whether Krasa's Brundibar won the competition, or whether it was excluded from the competition, or whether the competition was ever concluded. A few months after the opera was completed, the German army invaded and occupied Czechoslovakia, and Krasa, being Jewish, would have been barred from participation in such a contest, Jewish music having been declared unperformable before a general audience by Nazi race laws.

Brundibar was not given its premiere until 1942, at the Vinohrady, a Jewish boys' orphanage, which had become a concert and recital hall for the Jews of the Prague ghetto. The piece was given three performances before the Nazis rounded up the opera's designer, conductor, director and accompanist, all the boys in the orphanage, and Krasa. All were transported to the concentration camp at Terezin.

In September 1943, this same group, all inmates of Terezin, staged a new, co-ed production of Brundibar using the camp's imprisoned children. Krasa brilliantly orchestrated the piano score for a small ensemble, taking advantage of the fact that some of Czechoslovakia's best musicians were prisoners in Terezin. The opera became a hit among the inmate population. Brundibar is a political allegory, an almost undisguised cry for resistance to Hitler. In photos of the production, the boy playing the organ grinder, Brundibar, is wearing a moustache.

Brundibar was performed 55 times at Terezin. Jews sang it for Jews during the Freizeitgestaltung, or "free time period", the Nazis permitted the inmates of Terezin. Paradoxically, before long the camp officials recognised the opera's propaganda potential. It was performed for the International Red Cross representative sent to inspect camp conditions, who went away impressed with the kindness of the Nazis and the cultured atmosphere of the camp. Segments of a performance were then filmed for inclusion in the Nazi-produced documentary, Der Führer Schenkt Den Juden Eine Stadt (The Fuhrer Gives The Jews A City).

Nearly all the children who performed it were eventually sent to Auschwitz, where they were murdered. Krasa was killed there in October 1944.

Maurice, Michael di Capua and I have struggled to make a children's book out of Brundibar, one that honours the martyred dead. Our discussions have raised the question: in a world of trouble and woe and worse, what are children to be told? How much do they need to know so that they are prepared to meet the world? How much can they handle, and at what point does truth, when it is terrible, faith-destroying, hope-destroying, unassimilable truth, become unsuitable for children, with their still undeveloped capacities to sustain its reception?

I've been moved and have felt privileged to observe first hand how deeply Maurice suffers a picture book. He drew Brundibar twice; he produced an entire set of sketches and then, losing faith in the approach he had taken, considered abandoning the book. Jules Feiffer, having heard what a rough time his old friend was having, called Maurice to tell him about some new watercolour pens he'd just bought. He wanted Maurice to try them. It was intended, Jules told me, as "a kick in the ass". It worked. Maurice began again, with remarkable results.

One of our discussions centred around the character of Brundibar, played on stage by a boy but intended to represent Hitler himself. Maurice's first impulse was to draw the organ grinder as Hitler. We agonised over the results. It was too horrible, and it raised all the old questions. When you are reading this book to a child, are you meant to stop and explain to the kid who this scary-looking man was, or what he'd done? I felt the choice we'd made was unfair to parents, and inappropriate to the tale, to the impulse to present an allegory. So we turned Brundibar to Hitler in a clown costume. Still it seemed wrong; in the opera, Brundibar is a boy, bigger than the two protagonists but not as formidable a foe as an adult would be; and again, was it right to play hide-and-seek with Hilter's visage, an icon of human evil? Maurice went back to work and made the decision to turn Brundibar back into a boy; to give him Napoleon's hat; to festoon his upper lip with a moustache that threatens to become rat's whiskers; and finally, to put into the boy's head staring eyes of psychopathic blue.

As a way of addressing our concerns about the tale and its history, Maurice evolved a narrative strategy for Brundibar. He explained to me that the story's first part - Aninku and Pepicek going to fetch milk for their mother, their inability to get it, their terrified retreat - was to be taken at face value. Our readers were meant to understand that this part relates the story exactly as it happened. The story's second part - the children's rescue, their triumph - was possibly real, or possibly merely a victory dreamt by two cold, homeless kids for whom the morning will bring no good news. Possibly it's our wish that everything will work out for them, even as we know that often it doesn't.

But his Brundibar illustrations seem to describe a path that diverges from his own strategy. The first images, those in the "real" part of the book, are brightly coloured. They're folk drawings, almost - God forbid I should say they're done in a "fat" style. After the kids hide in the alley and meet their animal rescuers, Maurice's drawings assume a greater degree of elaboration, historical specificity, of gritty reality. The triumph, which he grievingly reads as an improbable wish, appears paradoxically to be more real, more substantial than the "reality" it flies away from. I don't think that Maurice devised this schematic in advance - he seemed rather surprised to notice he'd done it. It's an instinct for hope he has, a reflex for hope. It comes from his bones, or flows from his beleaguered heart, down to the fingertips of his soft, pale, subtle hands.

"I have to learn to live life, just enjoy it," he tells me on the telephone during a recent conversation. "I'm screaming at my enlarged prostate [and here he screams in a really unearthly voice], 'JUST SHUT THE FUCK UP!!!!' " Impressed by the sound he's made, he pauses. "I never heard that voice before." Then he concludes, "Anyway. That's what I have to learn. I must learn to unlearn appetite."

"So you think you can?" I ask. "That sounds difficult, and you're a hungry sort of person."

"I have to try," he says. "I should be ready to try. I've had a fat full life."

We make plans to see one another. He's not coming into the city! He hates New York at Christmas. The Rockefeller Centre tree summons up in him an empathic rage: "You've survived 500 years in the forest, you're the tallest, most beautiful thing in the whole forest, so our way of rewarding you for this? We cut you down and fly you to concrete and stick you in a pot and wrap 10,000 miles of electric bulbs around you!"

I tell him I will visit him in Connecticut. "Great," he says, "we can dance a kazatzkah!"

"What kind of a dance is that?" I ask.

"A kazatzkah is the Dance of Death," he tells me.

"Sounds good. Do you know the steps?" I ask.

"Do I know them? " he says with glee, making a kazatzkah sound like the most fun imaginable, "I know those steps in every notch, every noodle, every nerve cell! Of course I know them! I've been rehearsing them all my life!"

· This is an edited extract from Tony Kushner's book The Art Of Maurice Sendak: 1980 To The Present, to be published on December 9 by Abrams at £42. To order a copy for £38 (plus UK p&p), call the Guardian book service on 0870 066 7979.