After attractive young women, children are the most likely victims in a horror film. Their innocence is just too tempting for evil to pass up. Often in horror films children aren't brutally murdered, they're ... changed. Evil-y changed. Last night I watched The New Daughter (2009) starring Kevin Costner which I thought would be a silly movie but I actually genuinely enjoyed it. Like most child-in-horror films The New Daughter begins with a family split and a child acting out of the ordinary. The parent(s) initially chalk it up to a reaction to change but lo and behold it is much more sinister than that.
It is nearly always possession because there is nothing more jarring than an innocent becoming not innocent. Perhaps it is the reflex of our own neurosis that a child that is full of potential can be taken and turned to evil with little or no notice.Often times these "transgressive" possessions have to do with a re-population or a new evil being brought into the world (see The Last Exorcism) which seems inherent in the possession of a young girl as they physically ready to be mothers.For instance in The New Daughter, the evil forces at work are an ancient form of deity that lives in a kind of ant mount and takes young human girls to procreate. Sexuality is a kind of taboo subject (I find anyway) to deal with in these kinds of films. The New Daughter hints at this in some subtle yet provocative ways which I find intriguing because sexuality is a big step in any young person's life and then gaining acceptance for being a sexual person is an entirely different story. We have glimpse of this in The Exorcist as well when Regan gets friendly in with a crucifix and in a different way in Orphan. The notion of a person who is still a child being sexual is one of the most jarring and complicated issues that the first world deals with. Horror in particular deals with sexuality as a kind of fever that comes over people (I thinking specifically of the attempted date-rape in The Craft). In fact a lot of transgressive behavior in horror films comes as a reaction to the society we live in and having to conform and is there a more primal urge than that to procreate?
Your other form of evil comes in spawn of the Devil most famously depicted in The Omen and Rosemary's Baby. This is interesting because for most parents their child is their world, in these cases their child will end the world. In both films it's a struggle to deal with the concept and to finally (cough Gregory Peck cough) act on it. Lord knows a cute child actor saying Mommy or Daddy would melt even the blackest heart but we must stay strong ... otherwise that child might one day be Sam Neil and run for office.
I think the most enigmatic form of child possession is the just-to-fuck with you and your faith kind. We saw this most recently in the aptly titled The Possession and it is most famously in The Exorcist. A demon takes hold of a child and turns them into a strap 'em down and get some holy water kind of demon. This is the purest form of child possession in films because it plays off of their inherent innocence and turns them into beings capable of harm and peeing on carpets. They are taking the notion of your bright, friendly child becoming a sullen teenage and turning it into a morality tale. A "real-life" demon could be drugs, alcohol or sex. At some point parents stop knowing what their child is doing all the time which is the real worry.
And finally (in my estimation anyway) we have a sins-of-the-father possession. I think this is most clearly shown in Pet Sematary where the father's negligence is visited upon him when his dead infant son comes back to life. Moreover, in this context you could take it to mean the Founding Fathers as well with the ancient Indian burial ground playing a central role in this film.
Children are a great way to emphasize sin mainly because they are a reflection of ourselves. They offer up a clear and concise version of what kind of parent you are. And having to face yourself can be the scariest thing of all.