“When I tell parents how much sleep their preschooler needs, they’re always surprised,” says Kim West, LCSW-C, a child and family therapist known as The Sleep Lady. Three-year-olds need on average 12 hours of total shut-eye in 24 hours (including a 1.5-hour nap each day), while 4- and 5-year-olds need between 11 and 11.5 hours a night. But about a third of preschoolers don’t get the shut-eye they need, according to a National Sleep Foundation survey. Overly tired tots have more meltdowns, says West, and their attention spans are shorter and they’re less flexible and adaptable. When toddlers are overtired they don’t do as well with changes and transitions, such as a new baby sitter or teacher, or trying new things, such as a new food. One sure sign your child’s exhausted: If he nods off every time he rides in the car.