I think that the ending is a sad one, a horrific conclusion to the family's narrative. Yet, I think it is completely justifiable. There is really no other way in my mind to frame what happens to the family when they are so guided by fear. The paranoia of the family of the outside world is one in which few opportunities for happiness are evident. The insulated and inward view of the world is one in which there can be no enrichment, no enhancement of opportunity. Rather, it is one that slowly chokes the life out of living. It is not surprising that the boy dies because he is ensnared, trapped, by the jagged edges and the barbed wire. In much the same way, the husband and wife have suffocated one another and themselves with their irrational fear of the outside world. The ending is one in which the protagonists possess fear of "the other." This fear is what ends up crushing them and killing their son in the end. It makes sense that the ending is one that does not reward the family but rather illuminates how there can be little happiness if individuals shut themselves off from the world and prevent themselves from interacting with it through rational deliberation and open judgment.