We did the Eastern January 2004. We had perfect weather for swimming. The kids swam everyday. My husband and I also went in the water at a beach in St. Maarten and I had to get wet at CC, just to say I did so. CC was a little chilly. There were lots of people in the water, but I dove in once and it was enough for me.
What was really nice is our DD 4 and DS 2 could play all day in the sand and it wasn't too hot.
Enjoy your cruise.