Each fall, as the preschool at the Barnard College Center for Toddler Development opens for a new year, there's a scene inside the classroom that goes something like this: Two-year-old Jeff enters with his face buried in his mother's skirt. His parents look almost as nervous as he does. Meanwhile Sara, also 2, bounds in without a glance back and giggles over the toys while her mother beams. Then there's Beth, 20 months, cautiously taking a few steps into the room while twin brother Sam grabs the door for dear life, crying hysterically. His dad says, "I don't know what's gotten into Sam. He seemed so excited." For the past 25 years, as the toddler center's associate director, I've seen every type of behavior as children and parents learn to say goodbye. But whether kids act shy, jump in headfirst, or weep during those first few days, I've learned that within a short time, almost all will feel comfortable.

Patricia Henderson Shimm is the coauthor, with Kate Ballen, of Parenting Your Toddler.