When we cruised in February, one family had a rude awakening about the arcade. They found out their kids had been swiping the KTTW card at the arcade to buy arcade cards and had run up quite a bill very quickly.
So, depending on the ages of your kids, you might want to eliminate charging privileges or use your card to get their arcade cards.
We bought our son his cards with the admonition that when they were gone, they were gone, so use them wisely!