From as young as 6 months old, babies find it funny when you or anyone else they've bonded with does something that's a little off, as when you pretend to drink from his bottle or you put a diaper on your arm. But at about 12 months, your child may try flipping reality on its head to make you laugh.
It starts when kids realize what wins attention, and since they crave it, they'll do what works again and again, says Paul McGhee, Ph.D., a developmental psychologist and author of Understanding and Promoting the Development of Children's Humor. Since 1-year-olds have a good idea of how objects work, they'll try misusing stuff for a laugh. So your kid may pretend his hairbrush is a phone and vice versa.
As they approach age 2, toddlers' understanding of words improves, and they start to use language to coax a smile out of you. Your child may point to his elbow when you say, "Show me your nose," for instance, or pick up a doll and call it a truck, simply to get a rise out of you.
Though his jokes may get old, your laugh will boost his comic confidence.