We did the Eastern Caribbean itinerary on the Fantasy in July. I traveled with my parents (40s), grandma (70), and sisters (11 and 16), so a little bit older than your group but I think the excursions we did would be great for any age.
In Tortola, we did Tour to Virgin Gorda (through Disney). It was the half-day trip to the Baths and a ton of fun. Our day started with a half-hour catamaran ride from Tortola to Virgin Gorda. From there, we got on open air safari-type vehicles for a brief tour of the island. Our guide gave us some history of the island and there was a photo stop. We were then transported to the top of the Baths. The walk from the drop-off area to the first beach is 350 yards, I believe the guide said. Based on what I had read, I was picturing a somewhat difficult hike. I didn't feel this was the case, however, as any steep areas generally had some stairs built into the sand. We had approximately 45 minutes at the first beach before the guides took anyone who wanted to go to the second beach through the caves. We all chose to go see the second beach. Again, I had read that going through the caves might be difficult for some but my grandma and very petite youngest sister had no problems. The second beach was even nicer than the first; we loved every minute of our time there. We did have a rather long hike back to the safari vehicles, however it was July in the Caribbean so we expected that part of the day to be warm. The catamaran ride back was pleasant and we were served water and punch.
In St. Thomas, we booked the Catamaran Sail, Snorkel, and Private Beach Club through Disney. When we got off the ship, we were greeted by one of our guides. He walked us down the pier to the catamaran, the Dancing Dolphin. Once onboard, we had a quick safety talk and then were free to move about the boat. The ride to Abi Beach was about 20 minutes. A note about this part of the day: there is no dock at Abi, the ship hands drop anchor a little ways off the beach. My sisters and I jumped into the water off the side of the boat, however they do have a set of stairs you can take into the water. My grandma and parents chose this option and the crew was more than happy to help with their bags so our camera didn't get wet. We had about two and a half hours to enjoy the beach, snorkel, etc. There was a sand volleyball court, sand toys, kayak/SUP rental, a bar (also served food I believe), bathrooms and a small gift shop. I can't rave about the crew highly enough. While snorkeling, I got a sea urchin stuck in my food (my fault, got too close to rocks they said to avoid). The crew was very attentive and made sure that I was okay/checked on me on the ride back to the dock. When our time at the beach was over, everyone boarded the catamaran and we took a harbor cruise. Water and rum punch were served and there was an opportunity to buy t-shirts. Despite the sea urchin incident, this excursion was my favorite part of our vacation.
Hope this helps. Please let me know if you have any questions. I can try to post pictures later if you are interested!
