I mess with their food on April Fools Day.
One year I made what looked like fancy mixed drinks in glass cups. It was Jell-o.
Another year I made cupcakes that looked like cheeseburgers and meatloaf/mashed potatoes that looked like cupcakes.
And then there was the blue milk on Percy Jackson't Birthday.
I tell y 6 year old when she doesn't want to take a shower, that, "Fine, I will only put you in head first. NOT feet first! I promise!"