I don't know how much difference you're talking about between categories. Even then it depends on how much time you'll plan to spend in your cabin and if you have any clostrophobia issues without a window. If it's a small diff, do it.
You have a good point about the kids account cars, I don't really know how they set up the cards for minors. You do want limits set though. I have a client who's kids went to the video arcade almost every day, all day. They didn't know there was a charge for their kids using the machines. The kids discovered sliding the card in the slot gave them credits. A very large bill at the end of the cruise and some long term grounded kiddos made for less than pleasant vacation memories.