We did this excursion last Oct. and took our 6 year old. The day we went the weather way beautiful (not windy) however the spot they took us to was a little rough for a small child. My DS and all the other children under the age of about 8 to 10 were having trouble and ended up spending the entire time on the boat...I would not recommend this unless your child is a strong swimmer or experienced snorkeler. For a 5 year old I would think snorkeling off the beach at CC would be better and less money.
Jennifer