Yes this is a terrible story as to the beating/discipline of a child.
I would like to agree with Poocher and Becky though that i would have cancelled my excursion. In no way am i saying what Carnival did was right, but after the first late excursion and fine and bad story from your son.....would have been cheaper for you to hire a nanny and pay her way on a cruise. It also seems funny that your husband REFUSEd to pay a $5 fine the second time. Should have paid it or signed for it and then disputed it later or when your credit card bill came in. All this for $5 ?....can't understand that rationale....
Hope you get a lawyer and have already taken photos of the abuse.