One fun thing to do with kids of all ages is spending a day at Xhel-ha which sells themselves as being a huge eco-village that you can experience. Sound weird? I thought so to until I went there and started snorkeling with parrot fish and sting rays--amoung other friendly creatures-- in their huge freshwater acquarium-like ponds. They have places where you can hike, see a dolphin show, listen to Jamican drummers, shop for knick-knacks, or borrow an inner-tube and catch a ride down their mile long lazy river.
I recommend buying a day package through the concierge at your hotel for about $40/adult. If you get the "all-inclusive" version, your towels, flippers, mask, and locker to place your gear is all ready payed for...plus you are given a brand new snorkel to take home as a souvenir! If you choose not to get this package, you'll end up having to rent all the above for far more than what you would have spent on a package.
Another ammenity that comes with the all-inclusive package is an all day pass to their all you can eat buffet. The food is delicious and they have an assortment to choose from. You'll be able to find anything you want from a plate of spaghetti, or grilled cheese sandwich, to a gourmet selection of tasty American and Mexican cuisines.
There are so many interesting things to see and experience at Xhel-ha that it is well worth it to spend a whole day there to tour the grounds and participate in all the activities. Come prepared to arrive early, spend the day being entertained, eat breakfast, lunch, and dinner on-site and get a load of great pictures to show all the folks back home.