Warning---if your child has charging priv., they can recharge their arcade card. THere have been situations of kids running up huge charges, and the parent is responsible.
Another way to do this is to cancel the child's charging. You give them an arcade card (which you got and charged on your KTTW). You can get the cards in $10 increments...any amount you want. You can reload the card any time you want using your KTTW card. You don't want to put too much on the card because if the child loses the arcade card, it is gone...unlike a KTTW which Guest Services can easily replace.