On our previous cruse, we had our 3 year old in a top bunk and she was just fine. She loved it up there actually. This left 1 bottom bed opened and unused aside from a place to place cloths.
We had connected state rooms for that one.
This upcoming cruise, I was able to upgrade for a slight amount and have a really great room (Empress 8664) But with that said, we initially booked an inside room and planned on just having the beds together and then switching if that was an issue with space.