I did an EC cruise on the Fantasy in September. My daughter was 14 months at that time.
Tortola: Originally, we had an independent catamaran charter booked for Tortola; however, we opted out of it because I messaged others on TripAdvisor (who did the same trip) and they advised it would be miserable with a child under the age of 5 - 6 years old. Instead we took a taxi to Cane Garden Bay and felt it was decent. I know a lot of people loved it, but I wasn't in love. You can get drinks and food there but I was glad to have packed a lunch for my daughter because the food you could order was mostly fried or not appealing.
St. Thomas: We took a taxi to Magen's Bay and I was absolutely in love with it! You do have to pay to get in - $5/per adult - but it was clean and safe. In the morning the beach was empty with it getting busier later in the day. If you get there early enough, you can snag a free picnic table rather than renting chairs or sitting in the sand. The restaurant offers a lot of variety like gyros, pizza, BLTs, hoagies, chicken fingers and also in the morning they had breakfast cooking. We walked the beach all the way down to the right hand side (if you faced the ocean) and there were tide pools and big boulders to climb on. I used it for great photo ops of my daughter. In the picture below you can also see darker spots in the water. This is a bed of seaweed/ocean grass. If you bring goggles you'll see lots of tiny little fish swimming. We also saw pelicans nose-diving into the water above it scooping up those tiny fish.
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