My 7 year old DS wanted to give it a try.
He may have been tired, but towards the end of the preshow, he stated forcefully, that he did NOT want to go on the ride.
We took our DS 7 and DD 6 out the "chicken door".
I don't recall anything practically scary in the preshow, but it took my DS several minutes to calm down after we left, and were back in the sunshine.
So far we have been lucky enough to go to WDW every couple of years.
I figure if they don't do things now, it will just leave more to do and discover later.
I feel it is better to skip a ride, then risk blowing a good part of the day, calming down a kid.
However, you just never know with kids.
I thought that they would be scared of Test Track. However, by the time they got to the fast loop, they had their hands in the air, and laughing out load.