I felt like the roller coaster was really intense and I think it would be scary for a 6 year old child. It goes backwards and the monster does pop out. If he really wants to do it and has his heart set on it, then I would let him do it but I do think it's a really intense ride.
I'm 23 and I was terrified on it!! On the flip side, I did see many young children ride the coaster and come off the ride with big smiles on their faces!