Some family traditions are heartwarming. Others are just plain fun -- like tricking Dad on April Fools' Day. Practical jokes are especially perfect for a preschooler, since she can simply watch them unfold, without needing to "get" a complicated punch line. They're even healthy for her development, says Robert R. Provine, Ph.D., author of Laughter: A Scientific Investigation. By turning the everyday on its head, your child's reminded of what's predictable in life. Some ways to be in cahoots with your kid:

Breakfast buffoonery. Let your kid add a bit of food coloring to milk, then watch her try to restrain herself when Dad pours it on his cereal.

Grooming giggles. Cover the bathroom mirror with plastic wrap -- then make sure your child is there to see the befuddled look on Dad's face.

Bathroom humor. Preschoolers think anything potty-related is absolutely hysterical. Go with it: Have your kid tell Dad the toilet's broken (as long as you're okay with him elaborating that "there's poop everywhere!").

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