Breakfast Bait and Switch
Swap out sugar for salt and watch Dad put it in his morning cup of coffee. (Have a second, non-salted cup ready to go though).
For more morning fun, take out cereal bags and put them in mismatching boxes. See how long it takes for everyone to find their favorite cereal.
Serve up a topsy-turvy dinner to throw your kids for a loop: bake meatloaf in a 12-cup muffin tin and frost with mashed potatoes for a "cupcakes" dinner -- bonus if you add food coloring to the spuds. Then toast strips of pound cake for a dessert of "French fries". Don't forget red-tinted frosting for ketchup!
If the Shoe Fits
Bunch up TP and stuff it in the toe of the victim's shoes. They'll wonder why their shoes suddenly don't fit.
DIY Daylight Saving Time
Set all the clocks in the house an hour or two early -- then ease the blow of an early wake-up by taking the kiddos out for breakfast
What do you do to create fun on April fools day?