As your toddler becomes more knowledgeable about how the world works, she'll start finding it funny to mix things up a little bit, says Alice Sterling Honig, Ph.D., professor emerita of child development at Syracuse University, in New York. So when she makes a joke, she's also showing off how smart she's getting: If she points to her elbow, tells you it's her nose, and falls over laughing, you'll know she has body parts pretty much figured out.
Her twists on everyday life might make you laugh, too -- just wait till she sticks her fake tiara on Daddy's head. But don't be surprised if she tells the same "joke" over and over -- and over. She doesn't quite get the concept of a stale joke yet. To get her giggling even more (and to keep it interesting for you), play along: When she says, "Mommy's a duck," go ahead and quack.