We did too-didn't have any issues.
We actually did this great snorkeling/stingray excursion when we went to Grand Cayman- we did not book it through Disney and it was great- we actually saw the boat full of cruise ship people at stingray city while we were there and it was PACKED- ours had plenty of room to spread out and lots of one on one with our crew! We used
www.captainmarvins.com/ My daughter was just under 4 when we went and she had such a blast snorkeling and with the stingrays. We still watch the video we bought from them of our trip!