DD is 9, almost 10, and her pocket money is $7 per week. We opened an account for her, and she must deposit a minimum $2 of her weekly pocket money. At christmas time she will be allowed to withdraw and buy something she wants.
We decided that by her having to deposit some of the money, then she can see where it goes and how she can earn interest on it, and hopefully she will learn a lesson on saving for something you want.

She usually puts the remaining money into her piggy bank and saves it for a new DS game anyway, so she is saving the majority of her money.