The baby on the spit...

This brutal image shows how easily something so innocent and powerless can be manipulated into something so vulgar by mankind alone. It contradicts the fact that a baby is Gods gift, now it has turned into nothing more than a pityful meal for the reckless monsters of the world. We as humans have created this miracle child, and yet the world has become so inhuman that those who've survived are prepared to eat it. Human-beings as we know them, who used to care for their world, are now extinct.
The fact that they left it to burn impacts the novel enormously, showing how everything that used to be holy in the world means nothing anymore, just left to burn like the rest of the world.
'...charred human infant headless and gutted and blackening on the spit.'
This disgusting image gives us the impression that nothing is sacred anymore; people have given up trying to find hope, which has drivin them to insanity.
As a father himself, it dearly pains him to see a child be abused in any state or form, giving us the impression that he empathises with the infancts unknown parents.
'...picked up the boy and started for the road with him, holding him close. I'm sorry, he whispered. I'm sorry'
In my opinion, he may not only be apologising to the child. He may be infact sharing his sorrow with the forgotten parents, himself being reminded of the realisation of how sacred his own child is. If he had gotten there earlier, he may have been able to stop this madness, yet, he himself knows he wouldn't have done such a thing because it would have caused unnecessary danger to themselves, therefore he is apologising to the parents.
To me, this event was obviously horrific, drawing out and intensifying once again the desperation of mankind. The world has forgotton to love and to cherish, the world each day becoming more bleak than the last, represented through the increasingly appaling events of the novel. I believe McCarthy was trying to evoke the same response to imply that as the novel becomes increasingly bleaker, the nearer to the end the characters are. McCarthy wants to give the characters a reason to keep on travelling; no'one wants to be eaten by savage cannibals, so they progress on.