Joan Heilbroner, best known for her first book, Robert the Rose Horse, which was published in 1962 and has never been out of print, is back. After a hiatus of about 20 years Heilbroner returns with A Pet Named Sneaker, which Julie Just of Janklow & Nesbit Associates has just sold to Alice Jonaitis at Random House. The book joins the house’s Beginner Books early reader series and will be published in spring 2013.

Now 89, but “still on fire,” as Just notes, Heilbroner brought Robert the Rose Horse to Dr. Seuss himself at Random House, back when he was the editor of Beginner Books. Illustrated by P.D. Eastman, the book has sold nearly 400,000 copies, it was the first of five children’s books written by Heilbroner; the others are Meet George Washington (which is part of the ever-popular Landmark series that dates back to the ’50s and early ’60s), Tom the TV Cat, This Is the House Where Jack Lives, and The Happy Birthday Present.

Like all of her books, Heilbroner says that the inspiration for A Pet Named Sneaker came from real-life. “I got the idea for Robert the Rose Horse because Fidel Castro was in town,” she recalls, “and there were police horses all over the city. That has nothing to do with my story, but the horses were the trigger.”

This time around the spark came from two of her grandchildren, Quentin and Katrina, who regaled their grandmother with an anecdote about their pet snake, Plato. “They were just crazy about that snake,” says Heilbroner, “and they would play with it endlessly, twisting and turning it. One day, Quentin and Katrina took it to a fair on Martha’s Vineyard and the fair director asked if the snake could do tricks. Quentin replied, ‘Certainly! He can make figure eights and handcuffs.’ ”

In Heilbroner’s book, Plato becomes Sneaker, because “the name Plato doesn’t mean anything to small children,” the author says. And instead of a fair, Sneaker is found in a pet store, where the funny tricks he does just might attract a boy enough to give him a home.

Heilbroner’s agent, Just, believes that her lasting popularity can be attributed to the fact that her books sprout from something real and therefore remain just as kid-friendly now as 20, 30, even 50 years ago. “All of Joan’s work still feels fresh,” says Just. “It’s not dated in any way.”

All manner of speculation could abound as to why Heilbroner had a fallow writing period for the last two decades, but in her case it was simply, as Just described, “a pause that went on.” Early on, it was often her young children, who were the source of inspiration; now it is her grandchildren. As her children grew older, Heilbroner wrote less often and, after receiving her M.L.S. from Columbia University, she became a school librarian in Manhattan. Upon her retirement, she was enjoying newfound leisure when the inspiration to write struck again.

Indeed, Heilbroner’s dry spell is over. Immediately after Sneaker was sold, she delivered another manuscript to Just, this one a Halloween story with characters that recall those in The Happy Birthday Present, also published in 1962 and still in print, nearly 50 years later.