Beware that depending on the time that you go Nassau can be cold in the winter months.
Some of the food is definitely expensive. It has been a few years but the breakfast buffet was like $25 per person. Some of the dinner places are about the same or more. You can get a burger by the pool for about $10 at lunch. There is a pizza place that is a little more budget friendly for dinner and a johnny rockets that isn't too expensive.
We never did a meal plan the two times that we went.
My kids were around that age the first time that we went. Check out the pool, splash pad, and lazy river by the coral towers (older part of the resort) my kids enjoyed it at that age. It was a nice break when the main splash pad got crowded. We did the dolphin petting thing once but I can't remember what the age restrictions are on that.
There is a liquor store, convenience store, and souvenir shops across the street from the marina to pick up stacks and milk. Anthony's Grill is in the same shopping center and is good.