Welcome aboard, Lindsay! My son was three when he sailed on his first Disney cruise, and believe me, it's a great age to enjoy everything Disney Cruise Line has to offer!
When you're viewing Port Adventures, choose a specific port, then look at the options on the left of the window. Check the age range of 0-2. This will narrow all the results to only those Port Adventures on which your son can join you. It always helps me to view only those that are actually available for our family's ages and go from there. You'll see there are quite a few in both St. Maarten and San Juan that are fun adventures for the whole family. Some are beach days, but others get you out to explore more of the culture and history of these unique ports of call. There are a few good ones in San Juan, but there are two in St. Maarten that I'd recommend for sure.
Your family would love the
St. Maarten Island and Butterfly Farm Tour. You'll get a great tour of the island, learning about different spots you pass, and you'll even have time to do some exploring and shopping on your own in Marigot. But your son will love the butterfly farm! Don't forget your camera!
Another adventure my daughter really loved was our semi-sub coral reef tour. In St. Maarten you can book the
Seaworld Explorer Coral Reef Exploration Tour. You'll climb down into the lower part of a semi-submersed watercraft and it'll feel like you're in a submarine, as you'll have portholes under the water to watch the gorgeous sea life and coral reef activities! Kids love having their own little underwater porthole to see the fish!
Have fun planning Lindsay!