No kids here, but did an Eastern Carib
DCL cruise last year that was originally scheduled to go to Tortola, but was rerouted to St Maarten due to the awful damage from the hurricanes in 2017, and then visited Tortola on a DCL sailing earlier this year.
We strongly preferred St. Maarten, and during our 2018 cruise, nearly every CM we talked to about the rerouting said they liked St. Maarten better too, and that we got lucky to get the different route. St. Maarten is the perfect port for just relaxing on the beach, no excursion needed. You do have to take a ferry boat to the main beach, which is a nominal fee, but once you get to the beach you can rent a couple of chairs and an umbrella, and they'll even bring you out a bucket of bottled waters or beers. It was the perfect lounge day, and I enjoyed the beautiful blue waters. It might be boring if you're looking for a more active day, but I'm certain there are excursions that would be more "exciting."
We like to wing it on our first trip to any port, so we didn't book an excursion in either port. There was very little to do in Tortola without having booked a prior excursion. There was a small shopping and dining area just where we got off the boat, and there were taxis you could pay to take you somewhere, but most of these didn't look particularly promising to us. If I want to do something far away from the dock, I like for it to be booked through Disney so I know that the person will actually come back to pick us up at the appointed time. So we walked around for a while, made it to a point where we would have to walk alongside a major road with no sidewalk, and decided to bail and head back to the ship (luckily we were able to enjoy our Senses Rainforest Passes while everyone else was ashore)!
I don't think either port is bad, I would just recommend booking an excursion if you visit Tortola. Think about what type of vacation you like to take, and decide if the St. Maarten day might be "too" laid-back for your kids? Have a great trip! Love the Eastern Caribbean cruises
