The only thing they are missing out on is the opportunity to brag to their classmates.  It really is a case of don't believe the hype. 

I've heard Epcot is OK, but Disney itself was no big whoop for me or my children.  There are better theme parks in the Orlando area that are a little less expensive.

And Cindy P probably has the best comment of all.  Contrived entertainment is OK once in a while, but I think kids and parents alike will get more out of a holiday that focuses on real things rather than illusions.