We took the public ferry (it leaves right next to the cruise dock and is about a 20 minute ride) to St George's Island to do Tobacco Bay beach. It's very sheltered so the water is shallow and calm and good for kids, though the water was quite cold when we went in October. We had an overnight in Bermuda on our cruise, so we did the National Museum of Bermuda on our second day, which is right next to the cruise port. The museum is part of a fort and the old Governor's house, and there is a nice big playground for kids, and they have dolphins right inside of the fort for a dolphin swim/experience. We didn't do that, but we spent some time watching them feeding/training the dolphins. It's an easy port to do on your own if you don't want to book excursions.