Hi there, Sandra!
The Disney Resort charging system enables each room to link its Keys to the World card to a single source of money for charging. The common approach is to use a credit card, of course, which is then charged for incidentals and expenses.
A credit card is definitely a great deal of responsibility for a child to handle, to be sure. The way around this is to give the Cast member at check-in a given amount of cash which will be linked to your account. While you lose the ability to have the credit card linked to the Key to the World, you will know that there is a finite pool of money from which your children can draw. This pool can, of course, be replenished at needed.
One option to consider, should you prefer having a credit card on file for your Keys to the World, is to provide your children with
Disney Gift Cards. When you purchase the card, you set the spending limit (and again, that can be added to easily at many locations throughout Walt Disney World). While they won't have the convenience of one-card carrying, you'll know that the chances of overspending or of issues on the credit card will be minimized. A lanyard with a card holder at the bottom - available all over Walt Disney World and
online) will help them keep their materials safe and close by.
Have a wonderful time on your trip!
see you later, celebrator,
-Deborah B.