It depends on the child. It can be quite intense but it's a wonderful amazing show.
I've taken DDs ages 1 & 4, 2 & 5, 4 & 7, and 5 & 8 and my youngest was afraid when she was one and a little nervous at 2 but she did fine. Now they love it and it's considered a highlight of the trip.
I say give it a try unless you think your kids won't like darkness, loud noise, villians on a screen and on the mountain and a tiny bit of fireworks. But the good outweighs the bad, IMHO.