This is one of the oddest movies I have ever seen. Fucked up parents raising children to be complete outsiders. With no knowledge of the world outside of their walls.
What even worse is that it seems that they don’t even have the ability to question things. Whatever their parents say is the ultimate truth. Even when the oldest (they have no names!) see those VHS films she repeats what she sees without being able to process what is happening.
She wants to get out and finds a disturbing way to do so. But like someone here pointed out in a comment, she doesn’t seem to know that there’s something more than just getting out of those walls.