Ok, here's my take on those. My kids, now 15, and 17 (the two who still talk about it to this day), say they were scared on SW. The witch turning around right in your face is kinda freaky. OF course they go on it now, and have no problem and can laugh- we go on it now to get the blacklight effect, cuz that's just plain cool. But really, I think it would make a big impact on a little guy Henry's age. ON THE OTHER HAND, I enjoyed it as a kid for as long as I remember, and although it was a little scary I enjoyed the adrenaline rush of the ride. So.... you just have to know your own child and how he reacts to say movies or other things like that.
HM is a whole nuther ball of wax. It is very dark, the music is intentionally spooky and there are LOTS of surprise pop-ups wtih REALLY loud noises that accompany the skeleton popping out. Again, you'd have to know Henry and his spook-tolerance. It is so delightfully full of fun sight gags and AMAZING, WAY ahead of their time special effects that I truly love the ride and have as long as I remember. I'd say a savvy 8 year old could really love it, especially if you talk about what to expect before riding it. It is one of those rides that is one of my earliest memories from DLR. I have never NOT liked it.

But I have seen dozens of kids crying to not go on it, and I think it is mean to force them on if they are THAT afraid. There's always another time when they are older and more able to handle it. Pushing is good to a point to help them face their fears, but is a fine line to dance. Each parent should know when they've crossed it.

That's just my 2 cents, and I know there's as many opinions on this as there are parents.