Knock Knock is a film that needs a chance. This is what is obviously going to earn hate. This movie seems confusing and according to other views, people don't really understand what is clearly put out there. This slasher focuses on a very dark origin for it's killer. The origin is sad and you feel sorry for him, which is a good thing.
The lead of this film is not any kid, okay, it's pretty damn obvious the lead is the Killer or if not the cop. The Kids are just the kills that the killer comes back to do.
Now when I watched this movie, I was confused at first and thought about turning it off, but please stick with it, as all the confusion fades and you get a crystal clear picture of why everything happens like it does.
If you like movies souly for senseless kills, then I suggest you go find some other (horrible) horror film then. This is a film you have to think to understand, and a movie that doesn't make you think isn't worth anything.