Add a little milk to this car, push a button and watch it go. Now mix in seltzer water or apple juice and see what happens. Formula Fuelers by Mattel ($19.99; ages 6 and up) are cars with motors capable of using various household fluids as fuel. Also included with the cars are Nitrox2™ liquid, tablets and powder which can be added to the creative concoctions. The goal is for kids to experiment with the various liquids in order to discover the fastest fuels. Mattel maintains that there is one optimal combination and that it is up for the kids to discover what that is. There are also Formula Fueler Motorcycles ($9.99) available.