I've been going on it since I was very young, long before videos existed. I've always loved it! I HATE the idea of showing someone a video of a ride before going! IMO, it defeats the fun of going in person. It is also likely to have the opposite of the intended effect.
As others have said, the ride is not especially designed to be scary. It has some amazing visual effects! The stretching room has always been one of my favorite parts!
As others have said, it depends on the attitude of both the child and the parent. It is not good to dismiss a child's concerns, nor is there benefit in teaching children to fear new experiences.
Overhyping the ride before you go just encourages fear. It is like the quote, "The lady doth protest too much, methinks." The best way to instill fear into a child is to make an issue of it before you arrive. Ugh!
Right now, the child doesn't fear what they've never seen.
It is much how the media and politicians operate. Ah...it is snow season, when every passing snowflake is hyped for maximum effect!