Surprisingly good, low budget gem.
You've probably seen the scenario before, kids go feral for some reason and the grown-ups have to survive. What makes this version good is the realistic character reactions. I read other reviews saying at the first sign of danger you would stop looking for your kids and just run. I call BS, or maybe I call someone who has never had kids. A halfway decent parent would not ditch their kids and run away! I would sacrifice my life and the life of anyone around me to save my kids! In a heartbeat. So suggesting that it would be more realistic for a parent to instantly believe a moody teenager that their children are now monsters, with no proof, is just crazy talk.
The tight plot very cleverly splits up the cast and only lets one character see what is really going on, creating doubt and misinformation, so no-one believes the poor teenager until it is too late, for most of the cast at least.
The tension builds consistently, and doesn't let up. There's enough gore and suspense to please more mature horror fans, but you have to go in expecting a slow build up. Also something weird was going on with the sound, I've read other reviews mention the same, so it wasn't just my copy. Turn the volume up, better yet wear headphones and let yourself get sucked in.