Hood & Larry,
On my Panama Canal cruise aboard MV Sun Princess last year, we had a Halloween party after the shows, so be sure to bring costumes. They also had a contest for the best costumes, with some fairly decent prizes for the top three (I received a rather nice brass mantle clock for third place). The judging seemed to award points for originality, creativity, and effort that went into making the costume, so a package costume from K-Mart probably won't win. Also, you can wear your costume to dinner.
I'm not sure what events they had for children and teens, as that would be up to the youth and teen counsellors.
BTW, our Halloween party fell on a casual night, but I'm not sure that it would have mattered since Halloween costumes probably would have been acceptable dress on that occasion regardless of the prescribed dress code.