My DH, 11DS, and I did SNUBA on our cruise. It was great!! My DS did not have one single problem and took to it like a "fish-in-water". My DH and I have our PADI cards and felt slightly restricted by the hose, but had a great time.
Our guide first went over some safety and use instructions with us. She even gave our DS a short verbal test to make sure he understood.

A tropical storm had moved through the area a few days earlier so the water was slightly cloudy. After about 15-20 minutes underwater we started to move to the ocean side of the reef, but the current was too strong. She said that she has never felt the current that strong, so we continued on the protected side of the reef. She felt that we were cheated (we never would have know ....

), so she gave us and the other family on the excursion (happened to be a DIS family also), a free copy of the photo CD. Great gift to compensate for the conditions!!
A few months ago, another DIS member asked about SNUBA. She and I emailed back and forth. She decided to rent SCUBA gear at Coki Beach and let her DS and Father SNUBA. She would be able to dive withthem, but not be restricted by the hoses.
If you have any questions, please feel free to send me a PM.