My son used to be quite shy, and would do things if his younger sister would do them too. But, last year he went on the pirate cruise and loved it. He was so excited about it, he asked if he could do it again the next day. I have read a lot of posts where shy kids just love this. The Castmembers are really wonderful on this and incorporate all the kids into the adventure. I say go for it, your child should love it.
Robin