I definitely think it is wrong to let minors watch these things.
While not a horror film the movie Magnum Force (C Eastwoo/D Harry) help inspire the HiFi murders out in Utah in the 70’s. The perps were 3 airmen who had seen the movie at the base theater the week before. I was stationed there (Hill AFB) when the murders occurred. The copied the drano scene from the beginning of the movie.
http://en.wikipedia.org/wiki/Hi-Fi_murders