We went to one of the last showings of POC on the 8/2 cruise. We thought that it would be empty because it had already been shown several times before. WRONG! The theatre was jam-packed.
DD and myself got seats, DH sat on the steps. Eventually, someone left and he got a seat.
As for Spy Kids 3-D and Chicago, they were pretty empty.
Finding Nemo was pretty full. They had a large section reserved for the kids club crowd.