Me: Child 2, go brush your teeth.
Child 2: But I'm too tired (repeat ~5 times)
Me: Do you want to go to the beach tomorrow?
Child 2: Yes!
Me: Then you'd better go brush your teeth.
Child 2: Why? What would happen?
Me (I'm not the one taking them to the beach tomorrow, and I won't even be around when they go, and he damn well knows this): UHHHhhhhhhhhh..... then, um.... you.... uh.... can't? go to the beach?
Child 2: Actually I will go to the beach tomorrow, but I'll go brush my teeth, anyway, or they'll get all rotten and fall out. Except these two (points). Because they're healthy and in the shade.