what reasonable parent would....?

I was thinking they did something to the parents at the parent indoctrination or whatever the father called it, when he was telling his soon that they had learned everything at the sisters school.

The smarmy doctor calming all fears with that fairytale story about his daughter. Maybe the parents were all stepfordized.

Who put the acid in my Spam?

I think that's the whole point of movies like this. Remember the whole Stepford series? There was Stepford wives, husbands and children.