On our last cruise, I bumped DD up to the 5 year old group. It was our 5th cruise (she had been in the 3-4 yr old group for the other four cruises) and she was turning 5 the day after we came back. DD is a very outgoing girl, but she was one of the youngest in the 5-7 year old group. If it was her first cruise, I would have let her stay in the 3-4 year old group. She tried making friends with the "older" kids, but she ended up hanging out with the counselors instead a lot. She had a blast, but that was due to the counselors.