My DS did this last year, he had just turned 5. He enjoyed it. It last about 2 hours, they have PB&J lunch, he got a pirate mickey ear's hat and a "treasure box" of trinkets at the end. Just a bunch of big rings, bracelets, coins, etc... etc....
DH and I went and rode some rides while he was on the cruise, they give you a beeper. I'd say if your child is interested, let them do it, the CM's are great with the kids. I'd call right away though, as they book VERY VERY quickly. I know we had to pay a deposit when we booked, I think they still do this. Anyway, if you know your dates, and want to do it, call and book SOON!!!!