Shouldn't your kids act that way whether or not there is a 'rule' about it? Isn't it the right thing to do to walk in the halls, play nicely in the pools, stand safely in the elevators? In fact, I don't think there is a 'rule' about not pushing all the elevator buttons, but it is a courtesy, and that's what you're teaching them, whether they are on a cruise or in your office building or a hotel. It doesn't matter that every other kid in the world is splashing or running or shouting - mine don't because it is the right way to behave not because there is a specific rule about it.
My kids are a little older (16 and 17) but it amazes me how many of their friends do not thank me for a ride or food or something else . My own kids thank me for picking them up from school or taking them to sports practice or taking them to restaurants --and
DCL cruises! Yes, each of them at separate times said 'thanks Mom' while we were on the cruise. These 'thank yous' took years of practice. I thank them for things, they thank me. Practice makes perfect. They know I'd be embarrassed if they failed to be polite while a guest in someone's home, including Mickey's home on the ship.
Nancy