I absolutely loved out day in Labadee, great beach day,nice BBQ lunch. YOu can just hang around and do nothing, or par take in many activities. We did the Waverunner excursion and it was a gas, husband even when and got on another one later in the day. Definitely sign up for this ASAP, even on-line at the RCCL web-site. The banana boat was going all day, parasailing and even some snorkeling, but I don't think the snorkeling was very good there. There is also a market area, where the locals sell their wares, some can be very agressive, so beware.
There is pleny of area to walk around to the other side, very windy and unsafe to swim, so stay in the water in their beach area. You can also rent a raft for $10 to use in the sand or in the water, loved that too! No, you can't get out of the RCCL are, in fact its totally fenced in and most likely not a good or safe idea to wonder out, but there is plenty of room to get away from it all if you like too.
I think the whole family will enjoy your day there, have fun!