Although the differences between the boy and his father and the cannibalistic and brutal men they encounter are more stark than the similarities, there are some things in common.  Both groups of people are survivors, doing their best to adjust and stay alive in a harsh and unwelcoming environment where weather and resources do little to help.  They both stick together, and are travelling in their separate groups, using each other to try to stay alive.  They both are results of the wars that have decimated the land and people around them--granted, they are on opposite spectrums of the results of war, but, they represent what can happen to mankind in such extreme situations.  They both do what they can to protect their own and to survive.

The differences are more clear--the boy and his father are not cannibals, not brutal murderers, not breeders of babies just to have meat to survive. They haven't abandoned their humanity, their decency and their respect for human lives other than their own.  They haven't completely caved into animalistic instincts, they don't represent all that is evil and cruel in the world, they aren't symbolic of what went wrong with the world in the first place.  They care for each other, they are decent and kind to one another, they still talk about God and keep morals and values alive in their lives.  They are surivors, but not barbarians.

All of this said, the boy is the most human, hopeful, kind and unscathed human in the story.  The father lets his survival instincts come above and beyond human kindness more often than the boy would like.  Granted, that instinct in the father probably is wise, but the boy still has compassion.  He hasn't seen life before the wars, then after; he wasn't grown enough to become bitter, hardened and disillusioned with mankind because of all of the destruction that they caused.  He still retains a childlike innocence and pure love for those who suffer.  He is young enough to not have the awfulness of the world that he lives in completely defeat him and his more compassionate human traits.  McCarthy uses the boy as a symbol of strength and hope in mankind, that, despite all of the evil that exists in the world, if there is but one flame of goodness left, life is worth living.

I hope that these thoughts help a bit; good luck!