We parents have this misguided idea that if we talk long enough, our children will agree with us and obey us with joy and gladness in their hearts. Ahh, no. Of course kids are going to ask why they can't do something and because teaching is an important part of parenting you should give them an answer...once. After that, it's time to stop talking, turn, walk away, and follow through. After a few times, you're going to make a believer out of them. Stop talking. Start doing.