I took my son when he was about 5 years old. He's the type that could put a movie in the vcr and he'd watch it for 90 minutes. He did great and was mesmerized by the entire show. He sat on the edge of his seat with his jaw open the entire show.
However, you know your child best...don't do it if you feel they will have "ants in their pants" because not only is it a waste of money for you but it's disturbing for the people around you. Although the show is highly entertaining, don't hype it up to your kids as a dance show...it's more/different than that.
If you go, enjoy! We loved it and I can't wait to go back. (but I have to wait till DS #2 gets rid of his "ants in his pants")