From the time Jesse Gardner of North Chelmsford, MA, was 3 months old, he loved to play with his mom's hair, especially as he fell asleep. When she got a shorter do, Jesse twirled his own hair as he nodded off.

Playing with hair is just one of the things a baby might do to comfort himself. Yours might rub his forehead or his toes or pull on his earlobe. This kind of self-soothing behavior is part of how children develop resilience, says Bob Sege, M.D., chief of general pediatrics at the Floating Hospital for Children at Tufts-New England Medical Center, in Boston.

You'll usually notice your baby tugging or rubbing when he's falling asleep or bored. "Babies have a limited number of things they can do to stimulate or calm themselves," explains Dr. Sege. For some kids, the behavior might last into preschool or beyond.