To you, a block is just a block, but put it in your toddler's hands and it becomes anything from a sandwich to a cruise ship. This may not seem like a major developmental milestone, but the ability to think symbolically is essential to learning language and math. "It's how children come to understand that letters stand for sounds and numbers represent amounts," says Jane M. Healy, PhD, author of Your Child's Growing Mind: Brain Development and Learning from Birth to Adolescence. Symbolic play also requires your kid to think abstractly, which helps him become a creative problem solver.
Your Role: At playtime, provide your toddler with simple toys and props such as dolls, old sheets and blankets, and pots and pans, that he can use in a variety of ways, says Doris Bergen, PhD, professor of educational psychology at Miami University, in Oxford, Ohio. (As you've probably noticed by now, even a simple cardboard box can keep him entertained for days, so give him that too!). Buying your child anything too realistic, such as a toy cell phone, limits his creativity, since he'll have a difficult time pretending it's something different.