Widely known for her bestselling adult fiction, including Good in Bed and Little Earthquakes, popular Philadelphia-based author Jennifer Weiner has written her first book for younger readers, the middle grade novel The Littlest Bigfoot (S&S/Aladdin, Sept.). The story features a misfit human girl, Alice, who rescues and then befriends a Bigfoot girl named Millie, whose hidden world Alice swears to protect. PW spoke with Weiner about the spark that fueled her kids’ book debut and other new projects, her take on how women and girls are perceived in society, and what’s next for her.

Why did you want to do a children’s book? How was that experience for you?

Well, people have been asking me for a long time about doing a children’s book and I had always said I wasn’t going to get into it with Jamie Lee Curtis and her people. And people were always asking me why I don’t write a YA book, and I’ve said to them that someone already wrote You Are SO Not Invited to My Bat Mitzvah, and my title had been taken. That was what I would have written and now it’s gone.

But, honestly, it was all about waiting until I had an idea. Then, a couple of years ago, my then-six-year-old [Phoebe, now eight] got really into Bigfoots and I was thinking about them, and thinking about her and my other daughter [Lucy, now 15], and the kinds of books I’d like them to be reading, and the kind of book I wished had been there when I was a girl.

The writing process was really very similar, but there were pieces of the editing process that were new. I had written this book to the same length as an adult novel and had too many characters, and too much plot and just too much going on. My editor said, “We have to figure out what to do here,” and that’s why it’s now a trilogy. I really did need to focus on the pacing more and write punchy, short chapters and cliffhanger endings and situations that would keep kids interested. I tried to write characters that felt familiar to kids, or even very different, but characters that would be compelling enough for kids to want to keep reading about them.

What is The Littlest Bigfoot about?

It’s basically about three misfit kids. Two of them are human and one is a Bigfoot. It’s about how they fit into their world, their families, their communities, and about being accepted, understood, and appreciated for what they bring to the table. They’re trying to figure all that out.

You write and speak passionately about how women see themselves, and society’s messages to women—including your recent #weartheswimsuit posts and an August 26 New York Times op-ed piece about body image. Is there a broader message addressing any of those things in The Littlest Bigfoot that you hope will resonate with readers?

I don’t ever want to write a message story or be didactic or have readers feel that I’m hitting them over the head with my politics or whatever. But, as I said, I have daughters and I think about the world they are growing up in, and what they are seeing and learning about what they are valued for. In the book, I wanted to create this culture where size is privilege and being big and strong is a good thing, and being small and delicate really isn’t. I hope girls will see how arbitrary all this is. It all depends on where you are in a culture, where you are in the world. It’s an old chestnut that looks don’t define you, and it’s more important to ask, “Are you loyal? Are you kind? Are you smart? Are you brave?” I don’t think girls can hear enough that it’s not what they look like, but who they are as people, that matters.

Do your daughters see you in a different light now that you’ve written something for readers closer to their ages?

It’s funny. We had company the other day; a friend of mine and her daughters came over. And one of the girls was so excited to get a copy of the book. “I can’t wait to read it! I’ve been waiting all summer! I can’t wait to find out if it’s different now!” She had been in my daughter’s class when I read the book aloud to them in its earlier stages. And my daughter Phoebe was like, “eh.” No one is a hero to her own children.

Aside from The Littlest Bigfoot, you’ve also written your first memoir, Hungry Heart (Atria, Oct.). Is trying new things something that keeps your creative spark fresh as a writer? Or did something or someone coax you out of your comfort zone?

I think it’s always good to challenge yourself and do the thing that scares you. And both of these things scared me. With the children’s book, I wanted to see if I could pull it off and write a book that kids would be interested in. And with the nonfiction, that’s a collection of stories I had told on tour or at different speaking engagements at synagogues and other places over the years. But I had never sat down and written them down, put them in order, let my family read them—and that was scary! Novels are my first love and I don’t see a time when I won’t be excited to be working on something new. But these other new projects were a good stopping point. I was 45 when I was working on both of them, and it felt like a good halfway point in my life.

The Littlest Bigfoot is the first in a trilogy [the second title, Little Bigfoot, Big City, is due in 2017]. But is writing for younger readers something you’d like to continue beyond Alice and Millie’s story?

Interestingly, I’d been talking about not having an idea for a YA book, but now I think I have one. I’m going to write about when my mom came out.

I was getting ready to interview Judy Blume and I went back and read her whole oeuvre, everything I remembered reading as a kid. I was just thinking about all those situations, and how when those things would happen to me, I had a template, or a roadmap in her books. Then I was thinking about what it was like when my mom came out. I thought, “Judy, where was your book about that?” And I thought, probably I could try writing that book.

I had also been thinking about two couples we knew, where the moms and dads were really good friends and the families took vacations together and everything. Then the moms fell in love and they married each other. So those kids who’d been friends became stepsiblings. I thought God, what must that be like?

My story is about a girl who’s at the most awkward, uncertain time of her life when her mom drops this bomb on the family.

Do you have an idea when we might see that book? Is it under contract?

No it’s not under contract and I’m just talking about it with my editor at this point. It will be a while. Once I have an idea, it kind needs to sit for a while. We’re in the sitting phase now.

The Littlest Bigfoot by Jennifer Weiner. S&S/Aladdin, $16.99 Sept. ISBN 978-1-4814-7074-2