We did a Disney Cruise with our son, daughter-in-law and grandson and had a wonderful time. Our grandson was four and familiar with all the Disney characters; and as Cruise Fanatic said, there are plenty of adult areas so you should all have a good time.
Having said that, unless you and your son are huge Disney fans, and since you have all had good experiences already with Carnival, I can't see paying so much more for basically the same cruise. And judging from what you say, it sounds like your hubby already has a negative impression of the Disney experience. So my suggestion would be to stick with what you all know and like.