So many things wrong here...
***BEWARE: POSSIBLE SPOILERS!!!****
First...the parents are seeing blatant signs of pathology and psychosis, the mother is a psychologist herself, yet no real steps are taken to intervene and have the children partake in any kind of inpatient observation.
Second...the father, every single holiday, does all of that goofy stuff...dressing up like Santa...the Easter bunny...Halloween costumes. Maybe it's just me, but he came across as a complete goof. Completely Magoo.
Third, when the cat was found crucified, that would have been the END of it. The children are clearly and severely disturbed in some way and and need close observation in an inpatient facility. The mother is a PSYCHOLOGIST! Yet, nothing is done.
Fourth...who carries around a camcorder that often? How did the camera factor in as a priority...above just making the home safe, intervening with the children and dealing with this extremely serious situation? Why would the mother have taken the camera away with her when she was smoking in secret? Useless scene. Why would the husband have filmed himself drinking whiskey? To further the plot? Poor filmmaker judgement. Any good parent would have simply dropped the camera during each serious episode. I mean, screw the camera...tend to your crazy children!
Fifth, when the father was "exorcising" the children on the bed...there is no way those sheets tied on only ONE wrist of each child would have held them. You could actually see the little girl holding on to the "knot" so it wouldn't unravel. Where was the mother when this was going on? She only comes in after he's overpowered them both...tied them both up...and has performed the ritual on them.
While it kept my interest, the film is seriously flawed..and it was those flaws that upstaged the entire film itself. It was impossible to watch without keeping those flaws in mind the entire film. If obvious problems such as these keep ripping you out of the story...it ruins the experience.
The film had no real suspense...the character development was almost nil, thus removing any possibility of sympathetic feelings for any of them.
LASTLY, there is no way in HELL that Christian's mother would have allowed him to be with those children after they had so severely assaulted him in the church bathroom, biting him all over his body. No way, no how, end of story, FULL STOP. Fatal flaw in the plot.