Assumed this was based on a true story.

I swear to god I thought this was a fictionalized documentary when I was watching it.
I just kept expecting to see worse and worse examples of child abuse. And I cannot tell you how glad I was to see that the father wasn't raping his children at least.
The words on the front cover said 'Hilarious' and other things that lead me to believe that this was going to be a funny movie. But I was only horrified. Even when the girls were dancing I couldn't laugh. It was just so completely terrible and the fact that they didn't even know any better was really really sad.

After reading some commentary here about the movie, I see that it was supposed to be the depiction of some sort of utopia, but that's not the impression I got whatsoever.
I saw two manipulative people who decided to raise children cut off from the world so that mommy would never be left alone. They even went so far as to teach them wrong words so that if they ever got loose in the world, they could pretend that they kept them in seclusion because they were clearly crazy.

It was just really really sick. And that's how I felt at the end of the movie. The fact that the daughter wasn't causing a commotion in the trunk because she wanted out meant she had either died from blood loss or carbon monoxide poisoning. And I was kind of glad. Because that meant the father would have to suffer for what he did and the daughter wouldn't.