If you read through the posts in this thread there are several ideas for Coz. We're hopping a cab and going to Chankannab National Park. We did the dolphin excursion through
DCL last time, but this time we're just going on our own and snorkeling, watching the sea lion/manatee shows, etc. There's a lot to do there for not much $$.
I'm still trying to decide on Grand Cayman. I want to do the stingray city, but not sure the 4-yr old will be up for it. I might just go for it, and if she gets scared, she and I can hang out and watch the other two handling the rays! We used Capt. Marvin last time, but I've heard Moby Dick is really good.