First of all have a great time. Camp Carnival is wonderful. When my kids were younger they loved it and didn't want to leave. They couldn't wait for the next cruise so they could go back.
Grand Cayman: I would definitely do the Sting Ray City/Snorkel tour. If your children aren't strong swimmers they can wear a life vest. We used Soto's Cruises and had a great day with them. Other companies that have received good reviews are Captain Marvin's and Nativeways.
Cozumel: Not sure what will be open in Cozumel. We really like Chankanaab Park and have been there several times. I've booked several tours here through cozumelinsider.com. Sherri is great and will answer any question you have. They're right on the island and are very knowledgable. Our last trip our tour was cancelled due to Hurricane Katrina. They'd processed my refund before I even got home.
Ocho Rios: I would do a ship tour here. Dunns River Falls would be a good one to do.
Hope this helps and if you have any questions feel free to email me.