I agree with the above poster, about going during the day. At night, it can creep a kid out before they get there with the mood lighting, the sounds of wolves and the lightning strobes. During the day, it looks like just a fairly ordinary house (in DL) or just a shade creepy on the WDW side.
The soundtrack for
Disneyland's HM does have a long scream that on the CD they panned from left to right and then a loud crash. I don't remember this being in the Disney World version, but it probably is. It's been awhile since I've been on it. I think it's to distract you from the door opening to the Doombuggy loading area, maybe even to hide the noise of the motors.
I have heard people scream and in the tape I have of it, someone yelled "I can't breathe" when the Ghost Host mentioned the "No windows and no doors"
The story does get a bit creepier as the ride goes on, showing the different styles of two different imagineers that took different approaches on funny versus scary.
My best advice to any parent is not to force the kid into it and be aware of their phobias (dark, height, ghosts) and keep that in mind when taking them on it. I've seen so many parents drag a kid on a ride because they believe they'll really enjoy it only to see the kid miserable or freaked for the better part of the day. The point is, know your kids, and think of it in their eyes, rather than your own. Missing a ride is not as bad as having them freaked out all day, unable to enjoy other rides.