Somewhere between that first smile and that first recognizable syllable comes the magical sound of baby's first laughter. It may be a reaction to kisses on the belly, a tickling of toes, or a bouncy ride on Dad's knee. The triggers vary, but the laughter is inevitable. "In all cultures, it starts to develop in babies between 3 and 4 months," says Robert R. Provine, PhD, psychology professor at the University of Maryland, Baltimore County, and author of Laughter: A Scientific Investigation (Viking). That said, don't worry if you haven't heard guffaws by 4 months. "As with all milestones, some babies may laugh a little later," says Sheila Gahagan, MD, a clinical pediatrics professor at the University of Michigan's C.S. Mott Children's Hospital.What's So Funny?
While babies start laughing early, it's a long time before they'll appreciate a good joke. Meanwhile, what's likely to tickle their funny bones? "Young babies tend to find auditory and tactile things funny," says Dr. Gahagan. "Funny lip-popping sounds, a whispery noise, a squeaky voice, gentle blowing on their hair, or kisses on their tummy."
One of the first times Selena Pizzo, of Glastonbury, Connecticut, remembers her son, Jonathan, cracking up was when big sister, Ashley, snapped up the sun shade on her car window. "It rolled up quickly, making a clicking sound, and Jonathan, who was about 5 months, burst out laughing. One day, when he was cranky and crying, I asked Ashley to do the shade trick again, and it worked -- he immediately started laughing!" Of course, the things babies and toddlers find funny change as they grow, often reflecting the developmental tasks they're struggling with, explains Lawrence Kutner, PhD, co-director of the Harvard Medical School Center for Mental Health and Media.
Between 8 and 10 months, most babies delight in playing peekaboo, precisely because they're grappling with "object permanence," or the idea that things still exists, even when out of sight. "When you hide a toy or your face behind a cloth, it creates a certain tension for the baby, who is learning about object permanence," notes Kutner. "With infants, the game doesn't register. And for the older child who's already mastered object permanence, the game becomes boring."