In Parenting 101, I expect there would be a question therein that asks 'just how far would you go to protect your child?' And this is the main gist of this nonsensical tale.
The draw is almost certainly Michelle Monaghan, who does as best she can with what she's got but dressing this up as a horror is pushing credibility a little too far. Mother and two children move to a house in the middle of nowhere, surrounded by woods.
Trusty Labrador Pippin, being the smartest of those on show, clocks early on that something is not right about the woods and disappears when he goes bounding off to investigate. When comes back, he is not exactly man's best friend anymore and takes a meaty chunk out of the youngest child, who in turn then turns into a bloodsucking vampire.
It takes its sweet time getting even to this point, but when it does, it sets up the original question, as Monaghan has to somehow keep the child alive, without everyone finding out about his now peculiar dietary requirements. Lots of blood is spilt in one form another (rabbits, stolen plasma, dying old women, even the mothers own blood) in order to maintain this losing battle, and the reason for the whole problem takes something of a back step until the final act.
Largely unoriginal but Monaghan's stab at parenthood is an admirable one, even if it is equally unconvincing as the reason the whole mess got started in the first place. Whilst there is some closure, it probably won't satisfy anyone watching as there is a few too many strands dangling for most. On the long side and often dawdling, you could be forgiven for getting a little frustrated by the lack of savage bloodletting and perambulatory pace, if you're of that mindset.
It's okay as forgettable movie fodder, but there won't be many singing its praises and one viewing, honestly, will be enough.