How should parents control their children? Should they be allowed to earn money thereby risking them spending it on inappropriate things without parental knowledge? Until what age should a child be given an allowance? How much is an appropriate amount for allowance? How should children of various ages be disciplined when necessary?
I don’t think money is a stopper for items that you don’t want your children to have; they can always steal if they really want something. I believe the critical point is to communicate with your child and explain why your rules exist, and be up front about the rules. If your child has good reason to make an exception, accept it.