When we first saw it my sons were 2 and 5. We've been to Disney the past 4 years, and going back this summer. We have to see Fantasmic at least 2 times each trip. My family loves the villians though. If the kids are a little more nervous about things just sit farther back, it will be loud, but the experience is less intense.
Once I even sat adn held the videocamera the entire show, just to find out at the end I never hit the record button!!!