We have always liked Playa Mia. About 10 minutes from port, cab runs about 15.00. They have a water trampoline, kayaks, beach chairs etc. Plenty food and drink. They also have an area dedicated to snorkling with some replica ruins and statues under water. Not sure if they are open on Christmas Day.
Carnival Celebration 2003
Carnival Elation 2005
Carnival Conquest 2007
Royal Caribbean Rhapsody of the Seas 2009
Carnival Freedom 2010