In my previous cruises (10/07 and 7/09), my kids were given gift cards by their grandparents. But all the charging goes to the one account to the one credit card that is used by the parent(s). So, we put the disney gift cards as a payment on the account and the kids had to keep track of what they charged as to not go over that amount.
DCL will not put limits on their accounts. They either have charging privileges or no charging at all. My first cruise they boarded with charging privileges but then I had them removed - not because they went crazy with charging, but because I saw sooo many room keys (which are the charge cards) being left lying around on deck when kids were swimming etc. No one asked for ID when you charged, so I figured I'd rather be safe than sorry if someone wanted to take the kids cards and charge away.....