Hi Holly, welcome aboard! St. Thomas is a gorgeous island with so much to offer young families, and I don't just mean the beaches!
Though there are quite a few Port Adventures offered by Disney Cruise Line that include water activities and beach time, you might not have noticed the
Coral World and Butterfly Farm adventure. I would highly recommend this for your young family. The adults will get a bit of sight-seeing as you ride your motorcoach from the port to Coral World, and you'll have some beautiful views along the way. Once you arrive, the whole family will enjoy the undersea observatory, where you can see amazing sea life without having to strap on a snorkel or fins! While there is a bit of optional beach time included, you can choose to skip that and explore Coral World even more.
Then, hop back on your motorcoach to head to the Butterfly Garden. Again, the adults will enjoy the scenic drive with some historical information along the way, and once there, everyone will delight in seeing so many beautiful butterflies in this tropical paradise. There are shows there for kids, including a parrot show, as well as lots of learning opportunities.
Check out this port adventure, Holly. The cost is very reasonable for this exciting tour that is geared toward families. I hope you'll consider it. Then, if you want to do a little extra sight-seeing afterwards, there are shops in the port area within walking distance so you can enjoy a bit more of St. Thomas before heading back to the ship.
Please let me know if I can help with anything else before you set sail, Holly!