Kate Gosselin on Celebrating the Sextuplets' 13th Birthday Without Son Collin: 'It's a Bittersweet Moment'

More than two months have passed since the Gosselin sextuplets turned 13, and the festivities are unfolding on this season of Kate Plus 8.

On Monday’s episode, Kate Gosselin treated Aaden, Alexis, Hannah, Leah and Joel to a day of camping and glamping. The kids played a slew of games together including archery tag before enjoying a bonfire, s’mores and cake. Kate and her 16-year-old daughter Mady, who is twin to Cara, put their creative skills to the test decorating a large tent for the family.

But there was one notable absence: Kate’s 13-year-old son Collin, who has been enrolled in a program away from home to help him reach his full potential since last summer.

“Thirteen — need we say more?” said Kate, 42, during an on-camera confessional after the sextuplets, minus Collin, gathered around the table to blow out their candles on their separate cakes.

“The photos around the cake, I have them for every year, every child, every birthday,” explained Kate. “It’s definitely an iconic moment.”

“This year [was] much like last year,” she continued. “Obviously the difference is that Collin wasn’t there.”

“I am comforted with the fact that my kids, all of them, each unique child, is receiving exactly what they need and that hasn’t changed,” she said. “I’ve said that before, I’ll say it again. It’s a bittersweet moment [and] we’ve had many of them.”

“You can’t do anything without realizing he’s missing,” she added. “So we may not say it, but it’s always there.”

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Last August, Kate exclusively opened up to PEOPLE about how she came to the decision to enroll Collin in the program away from home, which she said “is helping him learn the skills he needs to be the best him he can be.”

“Collin has special needs,” the TLC star said. “[There’s] a fairly fluid diagnosis of what those needs are, but he needs to learn certain strategies to help him deal with things. This has been a struggle we’ve had for a very long time, and it’s one I’ve dealt with on my own. I’ve felt very alone in this. By the same token, it’s not something that has only impacted me or him – our entire family has been impacted.”

“We miss him so much, so it’s been hard because there is a huge hole in our family without him here,” she added. “But it comforts us to know he’s where he needs to be right now, and I can feel good about that.”

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In November, Kate told PEOPLE the program is helping Collin get “precisely what he needs.”

“I don’t know what the road ahead entails, but I’m very happy with the care that he’s getting, and am still completely comforted by the fact that he is so clearly exactly where he needs to be,” she said. “It comforts me as a mother — because when you, as a mom, can’t give your kids what they need, it is a huge comfort to find people who can.”

Kate Plus 8 airs Mondays (10 p.m. ET) on TLC.

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