I wouldn't recommend a "kid" ever have a credit card. 18 is the legal age to apply for a credit card. NO one no matter what their age should ever have a credit card without a steady source of income.
I do however, have nothing against pre-paid or reloadable cards where you can only spend the amount available on the card. We have purchased these for our kids to school shop the last 3 years (they are 13 and 10 now) and it works really well because they can pick out their own items, swipe the card, and learn something in the process. As one person mentioned that cash teaches a child to live within their means, so does a pre-paid card, in fact even more so. Because they can use the card and then keep track of their spending and balances just like they will have to do as adults with credit cards and checks.