We didn't really do an excursion in Nassau... just walked around the shops a little bit with the strollers. Are you looking to spend time on a beach, or shop, or do something specific? We went back to the ship and the kids went to the pool and had a blast.
Flounders was great with our daughter (2 1/2). She had a great time - she had an accident and they even sent her clothes to the laundry for us, put her in a clean shirt, and had the clean clothes delivered back to us the next day. It wasn't crowded at all, and most of the time, the kids seemed happy to be watching videos or quietly playing. The characters also came to visit, as they gave us a Polaroid of her in Stitch's lap. Great shot!