seriously! My 4 year old dealt with it just fine...my 10 year old freaked out! Here are the things my older son took issue with:
1. The "fire" in the windows. He was in a panic about this. I wish I'd have warned him and explained that the fire is red light, a fan, and sheer drapes.
2. The shooting...again, I should have warned him. I think he would have been fine if he realized there actually isn't anything flying thru the air...it's air being shot up through the water that makes the splashes.
3. The drops. Well, not the drops, but the way they hide what's coming from you. Any time he couldn't see ahead of us, he became nearly frantic. The drops are very, very mild. They aren't even as challenging as going down the big slide at McDonalds...but because he didn't know what was coming, he hated it.
I'd say, find lots of pictures of the interior of the ride. Let your kids preview what they're going to see. You might get the music (it's on the 50th cd set) and let them listen to it, so they'll be familiar with that, too.
This ride is covered in depth in the guide books...you can get lots of facts and "look fors" to share with them.
I think both of your kids can probably handle it...but if they're at all skittish, prepare them well! You might, um, consider a small bribe. As in, there's a cool shop at the end of the ride where they can build their own necklaces or get t-shirts, lol!
For the adults, this is one ride you don't want to miss!