Rachel McAdams is sharing how motherhood influenced her latest film.

ET’s Rachel Smith spoke to McAdams at the screening of her new film, Are You There God? It’s Me, Margaret, based on the beloved novel by Judy Blume. In Blume’s hometown of Key West, Florida, McAdams exclusively caught up with ET and shared how she approached the movie as a mom.

“Coming to this as a mom was very different for me,” she shared. “To see through those eyes, you just remind yourself of what it was to be that age, and how hard it was. I’m like, ‘Oh, don’t worry about that stuff.’ But of course, you’re worrying about that stuff. That’s so sort of patronizing to say, ‘It’ll be fine.’ So, you gotta get back in your 12-year-old skin and realize how much everything mattered.”

McAdams, who plays Barbara Simon, the titular character’s mother continued, “So trying to do that when playing Barb, but at the same time, trying to be wise for this little girl, and be the big person and put my big girl pants on. And be a good role model too. It was interesting to have read the book as a mother and approach it from there.”

Originally published in 1970, Are You There God? It’s Me, Margaret became an unofficial guide for girls navigating adolescence and puberty throughout the second half of the 20th century. The book tells the story of 11-year-old Margaret Simon, the daughter of a Christian mother and Jewish father, who begins to feel uncomfortable with her lack of religious affiliation, also exacerbated by also having to deal with such issues as bras, menstruation and boys.

When asked what advice the 44-year-old actress would give her pre-teen self dealing with all those issues and more, McAdams said, “It’s gonna get easier. It gets really fun the older you get. I think it gets easier. I don’t know that I’d want to go back.”

She continued, “If I could go back with the wisdom, all the wisdom I have now, sure. But if just had to go right back? No way. No thank you.”

McAdams also shared some advice for the newest Regina George, Reneé Rapp, amid news of her casting in the Mean Girls musical movie, which kicked off production earlier this month.

“I don’t think she can do any wrong. She is amazing,” McAdams, who made the role famous in 2004 said. “She’s already got me beat with that voice. So, I’m just excited to see her incarnation. It’s such a great character. It’s so much fun to play, so, I hope she has a great time with it. And I can’t wait to see it.”

When asked if any of the OG plastics would come back for the musical movie iteration of the early aughts classic, McAdams said while she isn’t “in the works,” for the project, she would “never” say no to Tina Fey, “ever.”

“She’s the greatest. So, we’ll see how it all shakes out,” McAdams shared.