We just got back from the 7 day cruise from Boston to Bermuda. We traveled with my parents, my husband, our 7 and 2 year old and my brother/wife and his 3 year old. Overall, we had a fabulous time. I do recommend cruising (even with young children).
I did a lot of research prior to leaving on how to entertain my toddler since he was too young for the Splash Academy. I shouldn't have worried so much because it was a breeze keeping him entertained.
They have a room specifically for toddlers called the "guppy" room. It was awesome. They changed the toys out daily so it was always something new to play with. The 7 and 3 year old also enjoyed this room.
It was comfortable. We used the pack n play and push the beds against the wall. My only complaint would be the lights that did not work and the air conditioning problems. Our room was cleaned daily and we really enjoyed the towel animals!!