I haven't seen this show since my first visit to Disney. I remember being 'wowed' b/c they show you how they do some of those "tricks".
I also remember feeling the heat from the explosion of the plane. That might scare them a bit. But it depends on how your kids are. My son, when he was 2, would have been mezmerized by it. Yet, my daughter, when she was 2, probably would have clung to me a bit - b/c like you said, loud and such.
Check it out on YouTube if you want first -- it will give you an idea of the show itself so you can try and determine scariness, but it wont' of course let you hear how loud it is (I dont' remember it being any louder than other attractions at WDW).
Good luck!!