Laura Prepon on 2½-Year-Old Daughter's 'Primal' Reaction to New Baby: She 'Peed on Everything'

"We were trying not to laugh because we didn't want her to think it was okay for her to pee on her stuff, but it was so funny," says Laura Prepon

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Laura Prepon.

Laura Prepon's daughter Ella is a great big sister, but her first meeting with her baby brother was a little ... wet.

During a Friday call-in to Live with Kelly and Ryan, the actress talked about her new book You & I, as Mothers and revealed that she and husband Ben Foster tried to prep their 2½-year-old for her new sibling by helping her focus on an episode of one of her favorite television programs.

"She loves this show called Daniel Tiger and on his show, he got a new baby sister and we would try and explain it to her and be like, 'Daniel Tiger has a baby sister, you're gonna have a baby brother,' " said Prepon, 40.

"So we really tried to get her to understand the concepts of it," added the Orange Is the New Black alum. "She understood it."

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But despite their preparations, things didn't go exactly as either Prepon or Foster, 39, could've imagined when they actually brought their now-4-month-old baby boy home.

"We brought him in to introduce him to our daughter and in her bedroom, we have this pretty cloth tepee — there's a bunch of blankets in it and stuffed animals, where she plays — and we brought the baby in and introduced them," said the new mother of two. "And it was the craziest thing — she ran into the tepee, took off all of her clothes, stared at us and just peed on everything."

"It was the most primal marking of territory," Prepon added with a laugh. "And we were trying not to laugh because we didn't want her to think it was okay for her to pee on her stuff, but it was so funny."

Luckily, Ella's reaction seemed to be just a one-time thing. "After that, it was just like, if he cries, she'll be upset — she's very empathetic. She wants to make sure he's good," said the star. "She was just proving a point. But it's great."

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Prepon announced the birth of her and Foster's second child in February, when PEOPLE confirmed the new addition was a boy. And in May, the former That '70s Show actress spoke to PEOPLE about why she and her husband haven't yet gone public with the name they gave their son.

"We make all those decisions as a family," said Prepon. "So at a certain point ... we'll say it, but ... being that we're in the public eye, we always have conversations around anything, especially that has to do with our kids. We're very protective of that."

She added that she and fellow actor Foster strive to "respect" the fact that their daughter and new son "aren't old enough to choose for themselves yet" whether they want to be shown on social media — but it doesn't mean the star thinks her family's way is the only way.

"Everyone is different with [posting] pictures of their kids — no judgment, do your thing. It's a personal thing," Prepon said. "But for my husband and I, that's where we do remain extra private, is when it comes to our kids."

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