Yes, the cruise ships do lots of special things on Christmas Eve and Day. Most of the activities are kid/family oriented. I recently wrote such an article for USA TODAY.com; click on their travel section; then look for the columnists to click on; scroll down until you see my name; you'll see a few cruise articles listed including the one on holidays at sea. There is a section there on Carnival.
Luisa Frey Gaynor
Family Cruise Editor