DS is really into April Fool's Day. I was planning on making meatloaf and mashed potato "cupcakes" for dinner and spaghetti "ice cream" (vanilla ice cream pushed through a ricer w/ strawberry sauce) for dessert. But DS has soccer practice and I won't be able to pull of a dinner like that. So I need a joke to play on him. Ideas?
Re: April Fool's joke on a 6-year-old
Does he use his underwear pocket? If so, sew it shut (DH's too!)
Shortsheet his bed (google it if you don't know how)
Mashed potatoes in his Oreo cookies.
My mom used to play pranks on my dad when he would go on business trips. Toothpaste in his oreo cookies (may not be safe for a kid), sew up the pocket in his underwear, replace his airline cigarettes with candy cigs (he smoked a pipe, but those were not allowed on international flights, but cigs were - go figure)... there were a ton of pranks, but I forget most of them now.

David "BD" 2/8/07 Spencer 9/12/11put food coloring in his milk, replace all his socks with dad's socks
This reminds me of the practical joke episode of Friends. They did the quarter thing, saran wrap on the toilet, etc. I don't really recommend those, though...
This site has a lot of cute ideas.