While the father may have some signs of PTSD, I don’t think that the son has or will have any signs of it. The mere fact that the boy was born after the destruction of the world removes him from our current labels that we associate with different things. Though he understands that things have changed since his father’s time, he has no capacity for understanding exactly how they have changed. The boy has no frame of reference for what we consider to be real afflictions in dealing with stress. While undoubtedly he is living in a stressful situation, or what would be to us, may not necessarily be to him. To him it is just the way that things are and have always been.
Children seem to take most everything they experience for the truth because they don’t know anything different. It’s only when they learn that there is something different is when the thought process and shame come into play. There is nothing different or shameful about the way the boy is living. It is the only truth he knows, and the only truth that seems to be out there for anyone else. It may be that after living with this new group of people he will learn or think that he and his father were living the “wrong” way. But it almost seems impossible in a world with no civilization that there could possibly be a wrong way to live save for eating people which these “good guys” take to be wrong as well. However, the boy still does not have the same frame of reference that we have for the world and the interpretation that we take from it when we read it is nothing like he is experiencing it. There is nothing to be stressed or really traumatized by because that is just the way things are at the end of the world.
Your post raises intriguing questions about the origins of our ethical bearing, of what we count as “good” or “bad.” It seems as if the boy has an innate sense of right and wrong…was this all taught to him by the man, or does the boy in fact have some residual connection with the older, pre-disaster world?