Where to go in florida in dec.?

im planning on goin to florida with my family in december.. I really wanted to take my kids to disney world but it looks like cocoa beach is too cold during dec to swim in the water. I want to be around the beach and have my kids enjoy the beach.. so i want to be around a place with a beach, kids things to do. But i also am takin a sitter so i want to be in a fun party place at the same time. where do i go?