This is an unexpectedly strong, inexpensive film. The basic premise—children behaving wildly and adults struggling to endure—is familiar territory. What elevates this movie is how believable the characters are. I've seen other critics claim that at the first indication of trouble, people would simply abandon their children and flee. I strongly disagree, or perhaps these reviewers have never been parents. A reasonable parent wouldn’t forsake their kids and escape! I’d gladly risk my own life, as well as the lives of those nearby, to protect my children—immediately. The story is carefully constructed, cleverly separating the characters and allowing only one person to grasp what's truly happening. This generates uncertainty and false information, so that no one trusts the troubled teen until it’s almost too late for most of them. The suspense steadily increases without relenting. There’s sufficient violence and anxiety to satisfy more experienced horror enthusiasts, but you should anticipate a gradual unfolding of events. I also noticed an oddity with the audio; other viewers have commented on this as well, so it wasn't specific to my version. Increase the volume, or even better, use headphones and allow yourself to become immersed in the experience.

Source on TMDB