Once we made the crossing it wasnt bad. Nassau was cold and cloudy thanks to a storm front, and everything was closed due to Boxing Day. Again this was all at the end of Dec. As for excursions, I cant really hlep you out since we had an almost 3 yr old. Long trips can be a bit much for him. My hubby, dad, and brother did the Thriller boat tour in Nassau depsite the rough waters and enjoyed it. My hubby and I have stayed at Atlantis (also went in Feb) so we werent interested in paying to do that. Plus, had our son seen the water slides, he wouldve been upset that he could use them or the pools (have to be a guest staying there). Didnt matter because the pools arent heated and were so cold in Feb hardly anyone was in them. Theyre nice in the summer though.
We were going to sign up to do a snorkel trip to St John at the last minute (it was booked so book your trips before or as soon as you board), then decided to do it on our own. We found out it was later cancelled since the seas were too rough. We instead did some shopping in town, then were directed to the Marriott Resort (can see from the ship on the point) for a beach stop. You can rent loungers and an umbrella, but it costs more for outsiders, and hotel guests get priority. It was enough to satisfy our sons beach craving though.
In St Maarten we were going to head over to Maho Beach to watch the planes come right over your head. Our son got ill the night before with ear infections/fever so we didnt venture far in the heat and strong sun. Yes even in winter its pretty hot and humid down there! Summer time you will probably see more storms later in the day, but they are usually short lived, and a brief welcome break from the humidity. My dad was going to take him so we could go (whole point was to take the little guy) but the taxi stand guy was not too nice and convinced us not to go in a rude way due to construction traffic. We ended up just getting the water taxi and walking around the shops. We are planning to go back to St Maarten on our own soon.
Thats the only stops we made. Sea days were a bit hard since our little one was too young for the kids club. We did go ice skating, and had he been older, our son wouldve done the rock wall (he did one in Aspen and loved it). The pools were too cold, but the hot tubs were too hot for once. He and I sat on the edge with our feet in though (I was preggo-still am). Once my idiot brother took our son to the arcade it was all over. It was the only place he wanted to go. He likes to pretend to play the games (for now). We couldnt even enjoy Johnny Rockets since its right next door and he learns his way around a ship pretty fast! Since youre going in the summer you shouldnt have a problem with cold weather and pools! Watch out for that sun though! Check the daily compass as theres always something going on. Dont miss the ice show. The only other shows we saw were the musicals since our son likes the lights and upbeat music, and Mickey Dolenz was performing one night (from the Monkees). We liked the show so much we saw it twice! Too bad Davy Jones wasnt along too!
Hope this helps some. Have a great trip!