Originally Posted by MrSelfDestruct

The way most of you explain it, it should be replaced with, "I already explained it." For the rest of situations, all it's going to do is either teach them to resent authoriy, or worse, to blindly obey orders without any consideration of the reasoning. xephrys' question of, "Do you know why ..." is also a much better solution. At the bare minimum, a child should know the logic behind a rule, even if they won't agree with it.