What Dr. Spock's Baby and Child Care is to mother, Pat the Bunny is to baby: required reading. Baby can't actually read the words, of course, but Pat isn't about words. Published 50 years ago this month, it was the original "touch-and-feel" book—and remains the genre's bestseller. "It's phenomenal," says Robin Warner, publisher of Golden Books, which sells 250,000 copies of Pat the Bunny each year. "A book that continues to be a classic."

Dorothy Kunhardt, who wrote 46 other children's books, created Bunny in the late '30s to bolster the family finances after her husband's textile company failed. She was "a genius at discovering what babies do," says her daughter Edith, who functioned as her mother's testing lab. It was baby Edith, born in 1937, who cooed with delight as she touched a fuzzy white silhouette of a cottontail, lifted a piece of blue cloth in a game of peekaboo, looked into a tiny mirror, touched Daddy's scratchy beard (actually, a piece of sandpaper), and put a finger through Mommy's (cardboard) ring. Since then, Pat the Bunny has been translated into four languages; it ranks second only to The Tale of Peter Rabbit in all-time sales.

Edith Kunhardt Davis, now 53, remembers her mother, who died in 1979 at the age of 77, as a writer with boundless curiosity. "She used to ride around with the garbagemen, taking notes," says Davis, herself a children's book author who wrote a sequel, Pat the Cat, in 1984. Davis admits that she and her three siblings were sometimes embarrassed by their mother's odd enthusiasms. But they also inherited the trait. "I find myself interviewing the milkman at 3 A.M.," Davis says.

Meanwhile, brother Philip Kunhardt, a former managing editor of LIFE, has grown used to the idea that in bookstores he's a minor celebrity. "The salespeople jump when they hear my name," he says. "They want to know about how my mother dreamed up the book. It seems as if it were pretty easy to dream up, but back then it wasn't." Philip has his own explanation for the book's continually strong sales. "It's a self-destructive book," he says. "Leave the baby alone with it, you'll find pages all over the place. Then you have to buy another for the next child."