We did Boatswain's in Grand Cayman - through
DCL. Did the whole tour of the facility and then we were able to snorkel and then swim/waterslide. Loved the whole thing - great experience.
In Costa Maya we booked our own snorkeling tour through
www.costa-maya-tours.com. This is the first time I've ever booked anything not through the cruise line, and I was so nervous, but it was FANTASTIC. It was just the 4 members of my family on a small boat, out to the reef to snorkel. The rep from the company sent specific, easy to follow instructions on how to get to him, and then he met us and walked us through the tour. It was really great and b/c it didn't come with age restrictions, my 4 year old was able to snorkel. Can't say enough good things about
www.costa-maya-tours.com!
Cozumel we went to Dolphinaris for the encounter. The kids loved it - it was the highlight of the week for them. Very well-organized. Prepare yourself to drop
loads of cash for pictures, though.
And then on Castaway we just enjoyed the beach and island, no excursions. Maybe next time!