NEW CANAAN — Katherine Paterson never set out to write children’s books, she came to the genre by chance.

“I didn’t really know who my first book was for,” Paterson said. “I sent it to publishers whose books I liked and it turns out I write for children or young people.”

“But when I write I’m not thinking of audience so much, I’m thinking of story,” added the 82-year-old author of “Bridge to Terabithia,” for which she won her first of two Newbery Medals, and countless other beloved children’s books.

Still, generations of children have responded to Paterson’s work. Since 1973, when her first novel, “The Sign of the Chrysanthemum,” was released, she has written more than 15 novels, many of which are still read widely.

On Oct. 19 at 6 p.m., Paterson, who resides in Vermont, will be in New Canaan — where her son, John, and grandchildren live — for the premiere of “The Great Gilly Hopkins,” an adaptation of her 1978 novel, sponsored by the New Canaan Library at the Playhouse Theater. Joining Paterson on the red carpet on Elm Street at the library’s fundraiser will be stars of the film, Clare Foley and Zachary Hernandez.

The story centers around a brash, 11-year-old girl named Gilly, who moves frequently between foster homes and hatches a plan to be reunited with her birth mother.

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Proceeds from this event benefit the Library’s Children’s Room. Tickets are $30 per person, $100 for a family of four and may be purchased online only at newcanaanlibrary.org/Gilly. The film is rated PG and children under 12 must be accompanied by an adult. Guests are invited to a pre-event pizza party for kids in the Library’s Lamb Room, starting at 4:30 p.m.

“All your characters come from within you, so you’re akin to all of them,” Paterson explained. Gilly’s character came to Paterson after she was asked to be a temporary foster parent in a crisis situation. That experience allowed her to imagine the feeling of adolescent homelessness.

Although Paterson didn’t begin writing until well into her adult life, she speculated that her many hours spent reading as a child created in her a specific point of view.

“Maybe because I read so much as a child I naturally gravitate to writing for children. I’m interested in writing the things that children are interested in. I don’t want to write about adultery and academia. I want to write about life and death and love and fear and jealousy,” Paterson said.

Those themes are evident in “The Great Gilly Hopkins.”

Leading up to the show, the New Canaan Library is encouraging those planning to attend to read the book. A 10 percent discount will be offered at Elm Street Books to anyone who mentions they will be at the premiere. Following the showing of the film, Paterson will stick around for a Question and Answer session.

“We’re so thrilled that Katherine is coming for this. She’s such an icon of children’s literature so it’s really an exciting event for the library,” said Ellen Crovato, the library’s director of development and marketing.

“We are just delighted to host the premiere of one of the great American children’s classics come to life on the big screen,” New Canaan Library Executive Director Lisa Oldham said. “It’s fabulous to share this story with a new generation of readers.”

Despite her success and countless devoted fans, Paterson said she is surprised by the continued popularity of her books.

“It’s sort of miraculous to me. I’m very grateful, of course, that generation after generation are reading the books. I think the human heart doesn’t change that much. I go deep inside myself when I write and the readers have been willing to come and meet me on that deep level. That’s the best I can explain,” Paterson said.

justin.papp@scni.com; @justinjpapp1