Clearly the behavior by the Carnival staff was atrocious. There is clearly no excuse for the treatment your husband received. I hope you took pictures of your daughter's back with the handprint on it. It would have been good evidence.
But what I find just as atrocious is the fact that the parents felt that their excursions were more important than the children. I agree with Poocher. If my kids were that uncomfortable going to Camp Carnival I would have cancelled my own excursions and spent the day with my kids doing my own thing. After what you described, I wouldn't have left my kids there. The staff had already displayed a bad attitude toward the parents.
If this wasn't supposed to be a "family" vacation why did you bother to take the kids along? And it sure doesn't sound like a "family" vacation to me.
There is NO excuse for the behavior of the staff. But...the parents need to accept the fact that they too had a part in this. I will probably be assaulted for this opinion but I don't care. The CHILDREN should have been the parents FIRST priority, not the adult excursions.