How can I teach my kids about saving money?

I gave a wallet to my child and he will put all his "hard-earned" money in it... allowance that he get from doing the chores... he will bring with him whenever we are out... he knows how much he has and really like to see it gets more and more in the wallet... he don't spend at all in each shopping trip... i hope he gets the idea of not spending the money even he can just open the wallet and take out the money anytime he wants... occasionally he will treat us drinks lol... :)