I remember Alex once brought up the fact that children today love to ask WHY, whenever they are told something. His answer to them is: "Why do you ask Why?" anticipating that they would not be able to reply.
I thought of this for a while. There are times where kids use "why" as an excuse, to which we could have better alternative answer than "Why do you ask why?". Such as "Because I, you father/mother/teacher, said so." Others ask in genuine sincerity, and we must reply with care.