I find it interesting that you describe the setting as "restricted" in your question. In my opinion, the setting in this excellent short story is anything but, except if you mean geographically. It is worth seriously examining the setting of this excellent short story and in particular how the setting contributes to the atmosphere. Greene is a master of description and this short story is no exception. Let us consider the setting as described at the beginning of the story:
The gang met every morning in an impromptu car-park, the site of the last bomb of the first blitz. On one side of the car-park leaned the first occupied house, number 3, of the shattered Northwood Terrace - literally leaned, for it had suffered from the blast of the bomb and the side walls were supported on wooden struts. A smaller bomb and some 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.
Clearly, the centre of the gang's world is a place of destruction. Descriptions such as "jagged tooth" to describe Old Misery's house clearly paint an image of the horrors of war, and we are forced to compare the setting to the beaten face of a human, with only one tooth left in his mouth. Cars parked where houses once stood creates a bleak atmosphere, symbolising moral desolation. This desolation is thus further developed and characterised in the figures of the boys, and especially of course in T., who is shown to express complete nihilism.
So, restricted it may be in terms of scope, but the narrow geographical focus on the bomb site only serves to strengthen the theme of the lives that the boys in the gang are living and how morally they are a bomb site as well.