I think that the most obvious aftermath of the war's bombings is the idea that there is destruction and decay all around the boys and their world. To a great extent, the boys have been weened on the destruction of war, the loss of life and property, and the idea that violence is a socially acceptable way of expressing emotions. Consider the description of the world that surrounds the boys, one that reflects an emptiness in both physicality and emotional connection:
The gang met every morning in an imprompty car- park, the site of the last bomb of the firs blitz... On one side of the car- park leant the first occupied house, No. 3, of the shattered Northwood Terrace- literally leant, for it had suffered from the blast of the bomb and the side walls were supported on wooden struts. A smaller bomb and incendiaries had fallen beyond, so that the house stuck up like a jagged tooth and carried on the further wall relics of its neighbour, a dado, the remains of a fireplace.
The aftermath of the war is intense in its physical remnants, but also in the fact that violence and destruction become a commonplace acceptance of reality. This creates the boys a disconnect between destructive actions and emotional affect. It is for this reason that they don't see the intrinsic wrong of destroying the old man's house, doing so in a methodical fashion with instructions and directives over a period of time. They have become the human embodiment of the war's destruction. There is a lack of affect about what they are doing, almost as if they have become the soulless force of destruction that the war is. This can be seen when the boys are burning Mr. Thomas' savings of notes:
"Of course I don't hate him,' T. said. 'There'd be no fun if I hated him. All this hate and love... It's soft. It's hooey. There's only things, Blackie."
This disconnect can be seen when they lock Mr. Thomas in the bathroom, but tell him that they don't want to hurt him in giving him a blanket. The aftermath of the war is one in which there is an gap between the of the boys' actions and the emotional effect of them. Greene uses the aftermath of the war to show how the exposure to endless violence and destruction can have a profound effect on children who begin to appropriate reality in the same manner.