We are probably considered "way too overprotective" with our DD8 & DS6. We've seen F! every summer since DS was almost 3 & DD was 6. To be honest, the first time it SCARED THEM TO DEATH! Each time since then, they just bury their heads in our laps/armpits during the scary parts.
It is very scary & intense with all of the flames, frightening music, & villains. If your children are used to seeing some of the scary Disney movies, then they may be okay. I know most people think we're wimps, but I just wanted to give you a pretty conservative point of view!
(I personally LOVE F! & we're not going to see it on our trip next week, which makes me sad.) 
Have fun regardless!