We stayed at the Carribean Beach Resort this year and they offered the cruise 2 or 3 mornings a week for ages 4-10 or 4-12 if I remember correctly. Parents were not allowed on board, however there were two pirate leaders that stayed with the children throughout the cruise. While we did not participate this year, I did see a few outings and I was most impressed at how well they looked after the kids and how much the kids seemed to be enjoying it. I am a crazy over-cautious parent (says DH) when it comes to letting the kids explore without me around, however, I would definately consider allowing DS6 and DD4 to participate next year. I was quite impressed by it.
There are a number of other resorts that do the cruise as well. CBR obviously stays within the resort waters, however, some other cruises go further from the resorts along the water-way to DTD.