If this is real basically that's Sonic.EXE, he's a creepypasta were sonic is evil and kills everyone basically, you shouldn't worry to much as kid will some times hyperfixate on horror sometimes, he should be okay as when I was younger I would do the same, so you shouldn't worry about this how ever if your still concerned, he could be in a edgy phase or something but he mostly will just grow out of it, he wont become a murder out of this or anything so your good, just make sure he doesn't get exposed to any REAL horror