Parable

I wish more people would get what you are saying, and quit arguing over all the literalistic interpretations. As Cormac McCarthy said in an interview with the Wall St. Journal, why the cataclysm happened isn't important. What's important is, given the situation, what do you do?
In his interview he said this story came from his own relationship with his 11 year old son, a "morally superior" boy who CM says was the original source of most of the lines attributed to the Boy in the story. C.M. also says he thinks "it's better to be good than to be smart."
To me, this is a parable about Good surviving in the almost overwhelming midst of Evil. The son is "the word of God." ("He said: If he is not the word of God God never spoke.") He represents and expresses Hope, Faith, and Love. The father, representing Everyman or "Us", although he himself doesn't feel he possesses those qualities in himself to the degree the Boy does, is trying to keep those values alive in a world that wants to destroy them. There are other Good Guys, and when We can no longer carry on and must give up our earthly struggle, the Faith/Hope/Love we kept alive will go on to survive with some other Good Guy.