You mention trundles, and then say you cant put your 2 year old "up there". Trundles are beds that are almost on the floor and roll under a regular twin bed and your ship has them and rollaways. You can also ask your cabin steward for a pack n play, which will fit into your inside cabin. More than likely you would have two uppers, if you book a quad .. I think thats what you are thinking of, bunk beds that come out of the wall.
The weight limit on the uppers is 250 lbs.
Iv never seen the water freezing in FL, but I lived south of your port, and we all like water different.. no heated pool.
You will have waterworks, where they slide into a splash of water, but I believe they have to be 48 inches tall to do the slide. One tiny pool. Salt water pumped in daily.
Majesty insides are 119 s.f. vs. 185 s.f on Carnival.