It really does depend on the kid. After my 9 yo nephew rode it the first time, he said never again. It was the scary stuff that got to him, not the coast aspect. After he say the Horror Makeup Show, he had a better understanding of special effects and he wanted to go back. He wound up riding about 6 more times, and wanted it to be the last ride before we left for home, but alas it was down due to technical difficulties.
I would suggest you ride it first without him. You should be a pretty good judge of whether or not it will be too much for him.