This kind of fantasy play is typical as toddlers approach age 2, says Susan Linn, a psychologist at Judge Baker Children's Center in Boston and Harvard Medical School.
Three big breakthroughs make this possible. First, kids start to notice differences in appearance. They also begin to understand symbols --that a doll can represent a real baby, for instance --and that they can pretend to be someone else without actually becoming that person.
Dressing up's also a crucial way for them to try new roles, rehearse real-life situations, and develop empathy --something they'll continue to do through imaginative play in the years to come. "Kids literally get to walk in other people's shoes," says Linn. (So don't freak out if your son is sporting a tiara or your little girl a necktie --it's normal for them to be curious about both genders.)
All it takes to get the fun going are time, space, and some hand-me-down clothes and accessories. Your child will feel the power of being someone else for a while --and you'll get some extremely cute pictures!