If the kids swim, certainly take them snorkeling! Make sure you book the StingRay City tour, the entire family will love it! In ocho Rios you can take everyone to Margaritaville for beach fun and shopping and if they are adventourous take them and clomb Dunns River Falls first.
Camp Carnival is excellant and the kids love it. Children are welcome in the dining room on every night but the dress code does apply to them as well and at the least let them wear a white shirt and tie. I have even seen some kids in tuxes! <