Today my 5 yr old designed a manned Mars rocket (while watching the Orion launch, why do you ask?), fussing quite a lot over fuels, colourcoding the electrical and life support systems, and drawing the innards of the rocket engine (which to be fair is simpler than, say, an automobile engine).

Then he put on his gloves to go outside and washed his hands. In that order.

DS1: Hon, you already finished your homework
DS2: Quit it with the protesting already!