A little boy and girl are in a bathtub, and are naked because they are too little too understand anything like that. The girl and boy ask each other: "What's that?" and they both reply: "I'll ask my parents."
So the boy goes home and asks his dad what it is. The dad looks solemnly at him and says: "Son, that's your car. You park it in a girls garage."
The girl goes home and says: "what's that?" The mother says: "That's your garage. dont let any boy park his car in it."
The next day they are again in the tub. The boy says its a car and remembers what his dad said. So he begins to put it in the girls "garage". But then the girl remembers what her mom said.
5 minutes later, the girl comes to the mom with blood all over her. The mother asks her what was wrong and she said: "Mommy, a boy tried to put his car in my garage, but I popped his two back tires."