Each workday morning Ann Martin climbs out of bed at 5:30, feeds the cat she calls Mouse and settles down to write a book. And each month she produces a best-seller. Her readers are not adults but the members of a mysterious species often sighted grazing at malls or giggling at sleep-overs—a secret society with a passion for friendship bracelets, baggy shirts and neon anything; a fickle fellowship marked by marathon phone calls, intense allegiances and whispered confidences.

Martin's devoted readers are little girls between the ages of 8 and 12: preteens for whom the next installment of The Babysitters Club is as coveted as a breakfast with Tiffany. No, make that Debbie Gibson. "Dear Ann," scrawled one giddy reader of what is currently the most successful juvenile paperback series in print, "I'm addicted.... I've memorized almost every part of every book and still can't stop.... Maybe there is a treatment center I can go to?"

Martin, 34, had no intention of creating an adolescent addiction when she left her publishing job at Bantam in 1985 to write children's books. "All I really wanted," she says, "was to publish two hardcovers a year and help support myself writing catalog copy, jacket blurbs, anything to make ends meet." Instead the editor-in-chief of Scholastic Inc., Jean Feiwel, created the Babysitters Club title and invited Martin to write it. What began in August 1986 as a miniseries is now a mini-industry, with 20 million books in print, among them a Babysitters Little Sister series and, twice a year, a superthick Baby-Sitters Super Special.

To supply the demand, Martin spends five hours a day, five days a week inventing adventures in the imaginary hamlet of Stoneybrook, Conn., where moms say 'drat,' kids never grow up, and family feuds are patched up before bedtime. The series centers on a clique of seven babysitters. Kristy, the leader, is modeled on Martin's best childhood friend, Beth Perkins; Mary Anne, the shy one, is a mirror image of the author.

Martin writes as if she has a passkey to the prewonder years. "There is a lot of Ann in her books," says Perkins. "She really cares about the words she writes and who she writes them for. She listens to kids and understands their sensitivity, like how it feels to wear the wrong-colored sneakers or be snubbed in the lunch line."

Martin's affinity for children is so finely tuned in part because she has such vivid memories of being a child. Her childhood in Princeton, N.J., was as cheerful as a Smiley-face sticker. A bashful, horse-crazy little girl, Ann and her younger sister, Jane, grew up at the edge of a forest in a household that was cluttered with books, pets and art supplies. Her father, a cartoonist, and mother, a nursery school teacher, encouraged creativity.

"I was moody and temperamental, but those were very happy years," she says, "because I had parents who would read to us, take us to circuses, teach us magic tricks and roast marshmallows in the woods with us. They never cared if we made a mess. My mother called our playroom 'toy soup.' "

"She always had projects," says Martin's mother, Edie. "One summer she organized a lending library of her books for the neighborhood children, and I remember one irate mother complaining because Ann had insisted that her child pay for an overdue book." Martin's favorite baby-sitter was the teenage boy who taught her to burp; her most bizarre sitting episode was keeping a weekend vigil over a neighbor's pet snake that, for reasons unknown to Ann, ended the weekend in a state of rigor mortis.

Martin survived that trauma, along with a phobia about gym class and an acute case of sibling rivalry. (Sister Jane, the family extrovert, currently works for Woody Allen as a production assistant and chats with Ann daily.) In 1977 she graduated with honors from Smith College, then taught children with special needs for a year before turning to publishing. She wrote three juvenile novels before taking on The Baby-Sitters Club.

A visit to her scrupulously tidy Manhattan apartment reveals that Martin has not left childhood completely behind. The rooms are filled with artifacts like the brown blob of hardened clay known as the Hamburger Man, which she fashioned when she was 5. A Pee-wee Herman doll has an honored place on her bed, and her kitchen is awash in kiddie drawings by the offspring of her close friends.

Though she delights in children, Martin—who is single and "not seeing anyone special at the moment"—is ambivalent about having them. "I really enjoy other people's kids," she says. "Right now there is not enough room in my life for one child and 15 books a year."

Martin reserves her mornings for writing in a windowless nook and her afternoons for editing manuscripts and reading mail—more than 7,000 letters a year. She can no longer answer every one but does save most of them, piling them in the closet. A quiet evening is often spent sewing beautiful clothes for her friends' children, and rarely does Martin drift to sleep without setting her VCR to tape David Letterman for viewing with breakfast.

Success has brought a new three-bedroom Greenwich Village apartment but few other extravagances. Martin continues to prefer coffee shops to fancy restaurants and buses to taxis. Instead she spends on others, sponsoring a Princeton student, supporting a dance program at an elementary school and donating toys to needy children each Christmas. "If anything, success has made her more serious," says Jean Feiwel, who collaborates on plots. "I tell her to take a deep breath and pretend she's Joan Collins, because that's who she is in a certain universe."

But Martin seems content to be Ann Martin. "I don't feel any different now than I did at 7," she says. "I don't want success to change things in any way. I'm very happy to get up on a particular day and know it will be the same as the day before. I want all my old friends and all my familiar things around me," she adds, "just as I did when I was a kid."