The Bobbsey Twins and Nancy Drew were too boring. And Trixie Belden? She was just plain dorky. But then Rebecca Langlois, a Dallas sixth-grader, discovered Kristy, Claudia, Mary Anne and Stacey. As just about every girl between eight and 12 knows, those are the founding members of the Baby-Sitters Club and the hottest fictional characters with today's preadolescent literary set. "They're funny and exciting, and the adventures they go through are stuff that can happen in real life," says Langlois, 12. She heads for the bookstore the minute the latest installment arrives.
That kind of devotion has sold more than 41...