Mine were 5 and 8 before we started cruising with them. However, I have read about folks bringing an inflatable baby pool if they had a balcony. Also, the umbrella strollers are easier to use than the larger strollers. Especially if you have a port that you are tendering into.
Our youngest son is a special needs child, so I always look like a walking pharmacy. I would suggest a med kit of the usual "baby meds stuff" just in case. Have a great cruise.