Call me crazy, but I kind of hate the idea of watching ride videos before going to WDW or any theme park. IMO, it kind of defeats the whole point of going.
Obviously, if you have a child with special needs, then it is fine to take extra precautions.
The whole point of WWD though is to experience a little adventure in a place that's reasonably safe. We should always pay attention to fire exits, for example.
Otherwise, the whole point of a theme park is to explore, especially the park that Walt built! Disney himself said it many times, and it is STILL repeated all over the parks.
I've been going to WDW since I was very little, long before the internet, and that excitement is the reason I'm still a fan!
When you see the thrill rides, it is very obvious that they are thrill rides. The best way, IMO, to help your child have a great time is simply to let them decide.
It is also okay to close your eyes once in a while.
I don't say all this because I was never afraid of any rides. I say all this because I feel empowered every time I brave a new attraction. It was true when I was three, and it was true when I braved FoP last month. I say: reward your child for being brave, never belittle them, and enjoy WDW together!