Over 25 years, actress and comedian Isla Fisher has played a variety of film and television characters, but her hands-on favorite role has always been that of mother to her three children with fellow comedian Sacha Baron Cohen. Their offspring set the stage for Fisher’s latest creative project: a middle grade series that debuts with Marge in Charge (HarperCollins, Oct.). The three stories in the book spotlight a zany babysitter who shows up at the door looking like a staid grandmother, but—literally—lets her rainbow hair down when left alone with siblings Jemima and Jake Button.

“I have always loved telling stories to my children, and doing silly voices, and Marge grew from that,” says Fisher. “Once I found the voice of Marge, the stories just flowed. In my experience, all kids love it when grownups misbehave and act wacky, and the naughtier I made Marge, while still keeping her responsible, the more my children responded. I think children make wonderful editors, because they are brutally honest.”

Marge’s adventures with her charges, which involve subverting the “to do” list that Mummy leaves behind, are fictional, but Fisher hints that the nanny’s character may have real-life roots. “If my two best friends had a love child, it would be Marge,” she says. “One of them is the eternal Peter Pan who is in total denial about reality, and the other tells magical, amazing tall tales.” Amid the wacky antics that abound in Marge in Charge, Fisher slips in some between-the-lines fodder. “Since Jemima is the eldest and feels she has to be a good girl, she is the perfect straight man for readers to relate to,” she says. “And when Marge misbehaves and acts silly, it’s not in an intentional or mean-spirited way. Rather, she unlocks the children’s creativity and challenges Jemima’s needing to follow the rules for rules’ sake.”

Fisher finds that being in front of the camera has informed being at the keyboard. “I suppose that acting has helped me to create strong characters that have an emotional arc, and to keep all the characters’ voices sounding different,” she remarks. “I love acting and writing equally,” she adds. “I get lost in both experiences—and I get to act out all the parts in my head as I am writing.”

Marge has more tricks up her sleeve. The nanny will return in Marge and the Pirate Baby and Marge and the Great Train Rescue—and might make subsequent appearances. “Marge is mischievous, ebullient, imaginative, kind, and fun, so when I am writing I get to live vicariously through her,” Fisher says. “ As long as these stories appeal to children, I will keep writing them.”

Today, 8–9:30 a.m. Isla Fisher is part of the Children’s Book and Author Breakfast, Special Events Hall.

Today, 10–11 a.m. Fisher signs in the ABA Members Lounge booth (721).