My son has done two of them so far. One at the Yacht Club and one at the Grand Floridian. He was 4 and 5 when he went and had an absolute blast! The stories they have are a little different but basically both times they were a group of maybe 8 kids with 2 cast members. The kids wore a black life vest with a skull and cross bones and got a pirate bandana to wear before boarding. They have some sort of story they tell and clues to find a treasure. They get a snack and drink while on the boat and get to keep a share of their treasure. It was mostly pirate rings, necklaces, fake jewels, etc. and they got a pirate keepsake bag to put it in.
I want to say both times we dropped him off around 9:15 and the boat departed around 9:30 and we were back to pick him up at 11am. He came bounding off the boat both times just crazy excited.