We did Snuba with our kids (ages 13 and 8) while in Key West.  This excursion is expensive ($118 for adults) and we were only in the water for about 20 minutes.  The water was frigid this time of year.  If you've got lean kids, they will have a hard time staying warm enough even in a wet suit.  The crew on the Snuba boat was nice, but the location we went to was disappointing.  We've been diving on shallow reefs off of Key West before and there are many more scenic places out there.  FYI - Snuba is just like scuba except the compressed air floats on rafts at the surface.  You will be in depths around 17 to 20 feet.  This experience was too hard for our 8 year old.  She did breathe through the regulator and put her head under the water but that was about all she could handle.  

Key West

If you choose to go to a beach in Cozumel and don't care about the open bar, buy your tickets at the beach.  We went to Playa Mia and spent $16/pp instead of $39/pp.  We still had access to beach chairs and all the non motorized water sports.  There are snacks and drinks available for cash purchase on site.

Cozumel

First, the Pros:  The staff on the Imagination is happy and helpful.The outside decks are pretty empty at night and it was easy to find a quiet romantic spot for star gazing.

Carnival Imagination Review

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