'Tough for mom': Kate Gosselin struggles with Collin missing birthday party for sextuplets on TLC show

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Kate Gosselin opened up about the pain of son Collin missing his 12th birthday party while getting treatment for his educational and social challenges.

The 41-year-old reality star on Tuesday's season premiere of Kate Plus 8 discussed Collin while throwing an elaborate scavenger hunt as her sextuplets turned 12 in May.  

Aaden, Alexis, Hannah, Leah, and Joel were all set to celebrate, but there was a clear missing spot as Collin was already away from home getting treatment. 

Sextuplets birthday: Kate Gosselin struggled with son Collin missing his 12th birthday party as her other sextuplets celebrated on Tuesday's season premiere of Kate Plus 8

'Obviously the major difference between this party and every other birthday party was the fact that Collin wasn't here,' Kate, 41, said as flashbacks from previous parties were shown.

The youngster's treatment has sparked controversy with dad Jon Gosselin threatening legal action, insisting even he does not know the whereabouts of his son.

However, Kate used the show to insist that she had no choice but to send Collin for help, without elaborating on either the kind of treatment or where he was.

'Throughout this last year he has really continued struggling,' she said in the episode filmed in May.

Getting treatment: Collin was away from his family getting treatment for social and educational issues

'It just became obvious to me that I was not able, with my own resources here, to meet his needs.

'He needs to be in an environment to help him learn the skills and gain the insight that he needs to be the best Collin that he can be,' Kate said.

She then admitted: 'So, birthday party without Collin - tough for them, tough for mom.'

Learning skills: Collin was shown briefly in the episode as the rest of the family prepared for the big birthday party

Tough time: Kate admitted that Collin's absence was tough on her

The episode saw the remaining sextuplets all enjoying a wild scavenger hunt that ended with a costume party, games and a piñata.

Kate admitted the hardest part came in cutting the cake - with her for the first time deciding not to sing the children individual renditions of Happy Birthday to avoid highlighting her son's absence.

'In years past, we've sung Happy Birthday six times and I ditched that this year,' she explained later.

One song: The mother of eight only sang Happy Birthday once this year instead of individual renditions

'I think for me that was the hardest part of the party.

'The activities of the day kept us busy. But singing to everyone as a group and Collin wasn't there grabbed me.'

After a pause, she continued: 'As it would … it was hard.'

Hardest party: Kate said the hardest part was singing to everyone without Collin there

She insisted she was doing the right thing by him, saying: 'I was comforted knowing that each of my children are receiving what they need. And the best of what they need and the best of what I can give them.

'It's good.'

As well as Collin's absence, the party also marked another milestone for Kate and the growth of her family.

New additions: The family also welcomed a pair of puppies into the mix

'The last year before the year of eight teenagers - the year I've been dreading… well, since they were all born,' she admitted.

Kate also appears to be trying out new parenting tactics, at least according to her eldest daughters, 16-year-old twins Cara and Mady, who helped her prepare for the party.

'She's trying out this new thing where instead of yelling she says things where she sounds disappointed in me,' Mady revealed.

The twins: Cara and Mady talked about Kate's new strategy of not yelling

'It's so bad because when I say ''stop yelling at me!'' and she goes, ''I'm not yelling.'' And I'm like, ''Yeah you are. You're just yelling in a quiet voice.''

'It's interesting that if I'm quiet it worries them more,' Kate smiled later.

The mom-of-eight bragged that she needed to go all-out for the party because her previous bashes had been so amazing.

Party supplies: Kate enlisted Cara and Mady to help shop for party supplies

Not yelling: Mady said that Kate's new thing was sounding disappointed instead of yelling

'When your kids and their friends every year say, ''That was the best birthday party ever!'' - so great to hear, but so much pressure,' she said.

After a mishap where she forgot to hide the second clue for the hunt, Kate had her children and their friends divided into separate groups of boys and girls with 'big black bus' for each group.

The clues then took them around local businesses their mom is friendly with, getting fresh clues to take them to the final party destination.

Scavenger hunt: The boys were lead to a local beef jerky business during the scavenger hunt

Kate drove the girls' team, and confidently admitted: 'We were kind of making jokes all day at the boys' expense.'

'I was, like, 98 percent sure that the girls were gonna win,' Mady admitted, before getting the shock of seeing the boys arrive at the final party spot first.

'When Aaden turned the corner I, like, actually screamed. I was, like, ''What the heck.'' I was so shocked.'

The map: Aaden and Joel tried to decipher the map together

'It was a crushing moment because I really felt that the girls would win,' admitted Kate.

She told the girls as they walked into the party: 'Inside you can think and feel the most horrible things you want. But out of your mouth comes ''Good game, well done.''

At the party, the kids dressed up to pose in a photo booth and also had a 'money booth' where they had to grab notes flying around in a wind machine that Kate said was 'extremely popular.'

Feeling confident: The girls were feeling confident they would get their first

'We probably could have kept them doing the money booth for the rest of the night,' she admitted.

They instead busted up a piñata and also cut a birthday cake decorated with the Scavenger Hunt map.

'I don't think any mom can have a birthday party for one child or six and not step back and realize, ''12 years ago my life changed'',' Kate said. 'For the better, six times.

Cool cake: The Scavenger Hunt Map was reproduced on the birthday cake

'They're taller, they're older - they're still my babies.'

Calling it her 'favoritist party ever,' she said it only adds to the pressure.

'I have to top this one now. I have a whole year to think about it,' she said with a sigh.

Growing fast: The sextuplets will become teenagers at next year's birthday party