Katherine Schwarzenegger Pratt Says Bond Between Her Daughters Is Just Like Her and Sister Christina

Katherine Schwarzenegger Pratt is celebrating sisterhood with her new children's book.

The author, animal rights activist and mom of two has announced her new children's book, Good Night, Sister. The picture book, to be released in February 2023 and now available for pre-order, is inspired by the bond the author had growing up with sister Christina Schwarzenegger, one that she's seeing again in a new light with her own daughters, Eloise Christina, 4 months, and Lyla Maria, 2.

Speaking with PEOPLE about the announcement, Katherine says she was inspired to write the book by her "wonderful memories, obviously of growing up with a sister but also just of my childhood in general."

"Since having my first daughter, my sister and I have reflected on many of the moments we spent together and the dynamic between us as sisters growing up," she shares, noting that though Christina is younger, she challenged "birth order" by trying things out before Katherine was ready to do so herself. "And so, to be able to put that in a book format was really special."

"The bedtime routine of reading stories with my parents is such a big part of what I do now with my own daughters. As I was doing this with my older daughter, Lyla, I wanted her to have a story that talked about sisterhood and the close bond, like what my sister and I had growing up and that we still have today."

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"I just value her presence in my life, and also in both my daughters' lives, so heavily that this book is a nice little tribute to that."

The host of Instagram Live series BDA Baby (Before, During, After Baby) has been thrilled to watch the bond between her own daughters grow since welcoming Eloise in May.

"It's really interesting because of course I'm a year and a half older than Christina, so I don't remember everything about when she came home from the hospital and our dynamic right away," she explains. "But my mom and dad say that it's very similar to the dynamic between Lyla and Eloise."

The mom of two says that Lyla fell into being a big sister almost immediately.

"Lyla took an interest in baby dolls right before I had Eloise, which was really perfect for me," she laughs. "So I think when I originally brought her home from the hospital it was very much like I was bringing home a real-life baby doll."

Katherine says her toddler is the "sweetest and most gentle, excited older sister" toward Eloise.

"She loves her and loves to spend time with her, and just to see their relationship forming already is really heartwarming and makes me really excited."

In addition to their two daughters, husband Chris Pratt is also dad to 9-year-old son Jack with ex Anna Farris. Katherine says the bond between Jack and his sisters reminds her of her own with younger brother Christopher Schwarzenegger.

"I'm eight years older than my youngest brother and Christopher was like my little baby, my real-life doll growing up," she recalls.

"I come from a big family and I love the idea of having a big family ourselves," she continues, noting that she and her Guardians of the Galaxy star husband "both love having kids around."

"Just to be able to see all the kids together is such a huge gift. We're really lucky that all the kids are awesome and get along so well and just love the heck out of each other."

Though this isn't Katherine's first foray into children's book, Good Night, Sister is the author's first release since becoming a mom.

"I was pregnant with Lyla when I launched my last book and so much has changed since then, in my life and also just in the world," she shares, noting that she didn't know the sex of her second baby at the time she'd finished writing the book, early in her second pregnancy.

"I'm really excited to make the memories of launching a children's book about sisters when I have two girls that are sisters and have my own sister."

Looking ahead to Eloise's first holiday season, Katherine says she's "into being able to make special memories, and really be present for all of those moments."

"I know everybody says it goes by so quickly, but it really does. And so I really just want to be present and just take it all in."