The Catastrophe Canyon part could possibly be scary for a young one, what with the "exploding" oil rig and truck with the resulting huge flames, and the cascading wall of water that at first appears that it will swamp the tram (it won't, but the people on the left side can get substantially splashed). If he can understand that this is all pretend, he may be okay. I don't recall anything else that would be scary for a child.