Coki Beach is wonderful for all. Coral World is right next door and a beautiful and easy way to see the underwater life in the Caribbean. There will be plenty of taxi to bring you back to the ship.
Be sure you tell the taxi driver to take you to and stop at Drake's Seat on the way back to the ship. It is one of the most beautiful spots in the Caribbean, as you are able to see most of the islands of the USVI's on a clear day, as well as Charlotte Amalie, Hassel Island and Water Island in the bay.
I have some pictures of Coki Beach, Coral World, and St. Thomas in my Webshots if you would like to see.