Julianne Moore is getting lots of buzz for her latest film, The Kids Are All Right

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Julianne Moore is getting lots of buzz for her latest film, The Kids Are All Right, but it’s a behind-the-scenes role that really has the actress excited these days.

Her first children’s book, Freckleface Strawberry, was recently adapted into an Off-Broadway musical, and premieres Friday in New York City.

“I’m really thrilled it’s happened,” Moore tells PEOPLE Moms & Babies of the book’s climb. “It absolutely came out of the blue — it was an utter and complete surprise to me.”

Rose Caiola, owner of the Manhattan Movement & Arts Center and Manhattan Youth Ballet, purchased Freckleface Strawberry for her own children a few years ago, and fell in love.

As luck would have it, she meet Moore soon after, and asked if she could take a crack at writing a show based on the book. After a watching a workshop performance (starring 24 children!) at the Movement & Arts Center in June 2009, Moore was sold. “The response was tremendous,” Caiola recalls, “so I decided to take it to the next level.”

Repurposing Freckleface Strawberry for the New York City stage required extensive casting — “our Freckleface, she fell out of heaven for us,” Caiola says — hiring musicians and creating colorful sets and costumes. “It was very challenging, yes,” Caiola recalls. “But it really worked out for us.”

Now, with the big premiere hours away, everyone’s feeling the butterflies, including Moore’s 8-year-old daughter, Liv Helen. “She came to the show with me recently, and it was fun,” Moore says. “She loved it, and really loved the characters. We talked a lot about what songs we liked, what characters we liked. She agreed with some of the things I said, too. It was a fun discussion … she was like, ‘Yeah mommy, yeah I think that too.’ “

Freckleface Strawberry is loosely based on Moore’s experiences as a child, when she was teased for her freckles and red hair. “I [wrote] it at the suggestion of a friend who said, ‘Oh you probably have something anecdotal about your childhood; you could write it down for your kids, they’d love it!’ “

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At the time, Moore laughed the idea off — “kids actually care very little about what you did as a kid,” she says — but the thought stuck with her. “I remember I was on a plane once, going to a job in London, and I wrote the story,” she recalls. “It all just happened really fast — it wasn’t anything intentional.” It led to a second book, Freckleface Strawberry and the Dodgeball Bully, two years later.

Though her 12½-year-old son Caleb hasn’t seen the show yet, he will join his mom at the New World Stages on opening night. “My children are wonderful, and they’re very proud of me and of the books,” Moore says. “We’re all very excited.”