On a blustery day last January, England's Prince William, 5, clambered to the top of a red antique fire engine, clamped on an old-fashioned fireman's helmet, clanged the bell and exuberantly yelled, ''Where's the fire?'' The scene captured in microcosm the delights and drawbacks of perhaps the most extraordinary childhood in the world. For while many children dream of becoming fire fighters when they grow up -- and in the meantime would gladly settle for a rampage in a station house -- the boy's play was a privileged but hardly spontaneous romp. Wills and his companions that day, younger brother Harry, 3, and cousins Peter and Zara Phillips (Princess Anne's children, 10 and 6 respectively), were clambering over a 1939 engine that once belonged to their great-grandfather, King George VI. And they were on display at a preplanned ''photo opportunity'' staged by Queen Elizabeth at her Sandringham estate in Norfolk for the benefit of a phalanx of photographers. The Queen's hope was that the press, sated, would then depart her 20,000-acre spread, leaving the family to enjoy its holiday privacy.

Her Majesty's ploy failed, and she was roundly criticized for pandering to the press and for her naivete in thinking she could rid herself of the paparazzi. After all, one day William will be swapping that aged helmet for an even rarer headpiece, the crown of the United Kingdom. That makes him one of the most curious creatures in the whole human zoo, the one whose difference from you and me isn't just a matter of money. What with palaces, toys galore and security guards, footmen and nannies at their every beck and call, not to mention entree into any school or club, the princes present their parents with the trickiest of tasks. It's up to Charles and Diana to master striking a balance between normality and nobility in the lives of the next generation of English royals.

How are Prince Charles and his princess, Diana, to inject a semblance of ordinariness into the lives of children who are so immensely privileged?

They try. Last Christmas, although she could easily have jumped the queue, Di stood with her two sons for 15 minutes at Selfridges, a London department store, waiting to visit with Santa. As Alison Morris, a fellow shopper and mother, put it, ''It was obvious she wanted her sons to be treated like other children.''

Despite her 180 official engagements last year throughout the United Kingdom and 17 days abroad on official trips, former kindergarten assistant Diana is very much a participatory mom. (No watching Starsky & Hutch, she has decreed -- too violent.) She relishes spending time with her children, playing with them in the nursery, reading them stories (''It's terribly important that parents should do this,'' she said last month) and dropping them off at school many mornings. She tries to oversee their evening bath, with help from Charles if he's at home (see box, page 120). And although he'll never be in a position to need it, Diana has made sure Wills gets a small amount of pocket money each week. She was apparently appalled to learn that even by the age of 8, Charles had no idea what half a crown (about 25 cents today) was worth.

Such small instructions in life's practicalities are replacing the sometimes harsh, stiff-upper-lip training that formerly was the lot of royals. Nannies, governesses and tutors, not parents, traditionally have raised the children of the British aristocracy. Queen Victoria seldom saw her small children for more than an hour a day, at which time they had been scrubbed and groomed and were on their best behavior.

Over the years, the royal approach to child-rearing didn't alter much, up to and including Charles's childhood. ''. . . never, not even as a baby, did he have his mother entirely to himself for any length of time,'' writes British author Penny Junor in her newly published biography, Charles. ''His mother saw him regularly for half an hour after breakfast, looked in on him briefly at lunchtime, and spent another half hour with him at the end of the day before he went to bed.''

Charles and Diana have broken this pattern. Whenever possible, they have tried to arrange their schedules around their children's rather than the other way around, even if this meant Charles's being late for an official engagement in order to see Wills bang the drums at his school Christmas concert or Di cutting short a visit to a milk-processing plant to pick Harry up from his first day of school. Di, in fact, refuses to leave her children for more than three weeks at a time and then makes a daily phone call.

Education is another matter. Charles, though he entered private school at age 8 (becoming the first heir to the throne to go outside the castle for lessons), had only a tutor until then -- and a rather lonely time of it. Di and Charles are hoping their sons will fare better by attending preschool with other children; the couple's decision to enroll the boys at Mrs. Mynors' Nursery School in London broke with tradition. Wills graduated last June and has moved on to Wetherby, a pre-prep school; Harry enrolled at Mrs. Mynors' this past September. The little princes' two nannies and five security men have been encouraged to take them to play -- with the children of commoners, even -- in public parks and to other amusements. Recently, for example, the boys visited the London Dungeon, where Harry and Wills spent an hour oohing and aahing over grisly exhibits of medieval torture instruments.

The boys' horror chamber tour made the next day's papers. Most of their excursions do. The reality to growing up royal in England today is that more press attention is paid to Wills and Harry than to any previous royal children (partly because of Mom's popularity). At the same time, security, thanks to the troubles in Northern Ireland and elsewhere, is tighter than ever. This makes visits to restaurants, shops and the cinema rare by the standards of normal children. Only for the sake of the boys' ''normalcy'' are they forthcoming at all. Last fall, for example, Di took Wills and Harry to see Snow White and the Seven Dwarfs at a Leicester Square cinema and then treated them to a lunch of hamburgers and ribs at the Chicago Rib Shack, an American- style restaurant in Knightsbridge.

The walls of Kensington Palace offer the family privacy and, according to Andrew Morton, author of Inside Kensington Palace, it is a child's paradise, with endless hallways in which to run and vast gardens for playing hide-and- seek. Morton suggests that the family's favorite spot is their railed roof garden, featuring a greenhouse (boasting clematis and miniature tomatoes) and ; a barbecue where Charles likes to grill salmon steaks, corn-on-the-cob and potatoes in foil, while Di sunbathes and the boys play on their slide-and- swing set.

The children's two-room nursery (one room for sleep, one for daytime play) is in the attic just above Charles and Di's bedroom. The boys have their own bathroom outfitted with child-size toilets and washbasin. Further along the corridor, nannies Ruth Wallace and Olga Powell have their own bed-sitting- room. Charles and Di, though early risers, writes Morton, awaken many a morning to the thump-thump-thump of vigorous play overhead. The nursery features furniture with hand-painted animals from Dragons, a posh London furniture store, and, according to Morton, ''all the usual toys -- cars, jigsaws, cuddly frogs and parrots, soldiers.'' There's also William's troop of foot-high soldiers in the nursery window, a rocking horse, compliments of Nancy Reagan, and Jumbo, the wheeled stuffed elephant, rescued from a palace basement, that once helped Prince Charles learn to walk. From their nursery windows (barred for safety) the boys can see the royal helicopter pad, a particular fascination for William, who imitates the ground crew's arm signals and knows the names of most of the Queen's pilots. One of his first words was ''plane.''

Weekends are spent at Highgrove, the Waleses' country house in Gloucestershire, and that's when Di and Charles really come into their own as parents, since they are busy with official duties while in London. For outdoor play there, Wills has a $40,000 miniature Jaguar (a present from the car's manufacturers) modeled after the XJS model his parents drive. There are also real live ponies; Wills's is named Trigger, Harry's is Smokey, and Diana, who shuns horses, showed her devotion by riding with her sons earlier this month while their father fished in Scotland.

Di does nearly all the boys' shopping, clothing them in OshKosh B'Gosh, Benetton and Absorba duds in these years before they have begun to learn the understated elegance of aristocratic English haberdashery. Holidays are spent with granny Elizabeth at Sandringham or Balmoral, or, in summer, visiting with the Spanish royal family in Majorca.

Wills already knows he is destined to be king -- he once tried to give orders to soldiers in the Royal Highland Fusiliers Regiment and threatened to sack them. Such behavior always brings a reprimand. Neither of the Waleses, however, enjoys the role of disciplinarian; that job is left to the boys' nannies and even their bodyguards, whom Diana has encouraged to correct the little princes' behavior when necessary.

Generally, it is Wills who gets corrected. He has a penchant for getting into royal snits when he doesn't get his way. Last fall he was brought home abruptly from a chum's birthday party after reportedly throwing a tantrum because he couldn't blow out the candles on the cake. He demonstrated his displeasure by throwing sandwiches and ice cream around the room. He cleaned up the mess, sulkily, only under great nanny duress. Harry, the opposite of Wills, is a sweet-natured, shy thumb-sucker. While Wills receives public scoldings from his nannies, Harry gets public cleanings after smearing chocolate, strawberries or whatever else he's eating on his face.

Sibling rivalry reportedly isn't much different at the palace than in any other home. The introverted Harry adores his older brother but resents reminders of Wills' greater skills; William protects his little brother but likes to be in charge. Press reports about the boys' differences, however, occasioned a skit on the satirical TV show Spitting Image last fall, which features grotesque puppets of the royal family and prominent politicians. A William puppet, dressed in combat gear, was shown attacking a Harry puppet with a knife and machine gun. The skit set off a public furor but reflected the common opinion in England that Wills's rambunctiousness may be too much for quiet Harry, who, at least initially, was too shy in nursery school to even speak to his teachers. Diana is sensitive to their different temperaments. ''She doesn't say to William, 'You should be more quiet like your brother,' or say to Harry, 'Get on with it, like William,' '' a palace observer reports. ''She treats them as completely separate people.''

She still has many years to help them find their own footing. Until they've completed their education, the little princes will have few official functions, and those only in the company of their parents. The Queen, with whom they take tea every Thursday afternoon, insists only that the two be present for family photo calls and holidays, but neither she nor their parents want the boys cutting ribbons and laying cornerstones. There will be time enough for that when they grow up, since the prospect of a ''real'' career for William, and even Harry, is remote at best. Any firm that employed one of the royals would certainly be suspected of unfair competition. Thus, despite all the efforts of their parents to make them feel ''normal,'' the reality is that the princes' lives, in the end, will be dictated by their birth. As Charles himself once said of his own realization that a monarchical future was inescapably his, ''I didn't wake up in my pram one day and say, 'Yippee!' I think it's something that dawns on you with the most ghastly, inexorable sense.'' How Prince William and Prince Harry handle the dawning of that realization will be of historic importance. They are being raised more like ''normal'' children than any royals before them, but they are destined to be forever set apart. These brief years of early childhood, in fact, will be the only period of relative normalcy they will ever know.

BOX: Lately, Charles chooses fishing over fathering

Ever since Wills's and Harry's births, when he set royal precedent by actually being there, Prince Charles has been lauded as a doting and involved dad. He helped bathe them, took them for nature appreciation walks and generally seemed to devote much more love and attention to his young children than had most previous royal dads, including his own father, Prince Philip. Lately though, as his interests (polo, fishing, gardening) and his wife's (dancing, shopping, pop music) have diverged, the family-man prince has frequently left the family behind to pursue his own agenda.

The first cracks in Charles's superdad image appeared last fall, when he logged an unprecedented 37 days straight apart from his family. Then came the three-week official visit with Diana to Australia and Thailand in late January, followed by his African safari in February. In March he made an American trip to give a speech in Pittsburgh and play polo in Palm Beach, then took a Swiss skiing vacation. It was in Switzerland that Charles nearly died in the avalanche that killed his good friend, Maj. Hugh Lindsay.

Though some said his recent fishing trip to Scotland was just what Charles needed after his loss, royal watchers were concerned that it meant leaving Di (no fisherwoman she) and the boys home at Highgrove during their school's Easter break. There was more concern when the British tabloids reported that Charles's fishing party of seven included Dale, Lady Tryon, an ex-flame (better known as ''Kanga'' because of her Australian birth). Her husband, Anthony, Lord Tryon, came along too, but this didn't keep Fleet Street from dubbing her Charles's ''blonde confidante.''

A veteran palace watcher dismisses the notion of a dalliance, saying, ''This fishing trip was arranged six months ago. Diana doesn't mind too much that he's gone off.'' Yet even this insider questions the wisdom of Charles's being away from his children so much, saying, ''It seems to be that he's with them when it suits him, not when it suits them.'' The hope is that being a dad will soon suit Charles once again.