I didn't realize your child couldn't get in the pool with a little swimmer pull-up on. But anyway, I wouldn't stress out before the cruise trying to accelerate potty training. Chances are that there will be some accidents anyway by being in a new environment and from all the excitement, etc. Just try alternate things activities and use the sprinklers if they have them on your ship. When in port, there's always the beach. Relax and have a good time. I'm sure you'll have a great time.Non potty trained children are not allowed in the watermark or sprinklers either.
49 nights with RCCL, 7 nights with Carnival, 11 nights with Disney, 14 nights with Princess, 45 nights with HAL