Hi Carlyn and welcome ! I can exactly ditto Penny's comments having done some of the same excursions of the islands. In Curacao we snorkled a sunken boat and the fish were many and varied in color..This also included a nice ride around the area with explanations by the crew prior to our snorkle. Taking the bus ride from ship to marina also afforded a nice tour of part of the island. Megan's Bay by taxi is an easy ride and Mom would probably enjoy this as there is some shad and the bay is calm..Not much in way of fish. Trunk Bay has my vote on best/most fish to see.
Enjoy your cruise. The kids can easily be kept busy on RCI ships.