Greene is careful to point towards the setting as a serious factor in producing a generation of children who have known nothing but war and destruction in their lives. Given this and the way that Old Misery's house stands up alone, it can almost be seen as an incitement to the boys. Note how the boys view their act of destruction:
Streaks of light came in through the closed shutters where they worked with the seriousness of creators - and destruction after all is a form of creation. A kind of imagination had seen this house as it had now become.
For the boys, and in particular for T., whose father, we are told, is an architect who has come down in the world, the destruction of the house allows them the chance to express their pent up anger, frustrations and experiences. Note how for T. in particular, he neither loves nor hates - life consists of "only things" to be destroyed. The postwar malaise combined with the boys' inability to find purpose in their lives results in this act of crime which gives them great satisfaction. Consider how T. is able to unite all the boys and help them achieve something "great" when before they were only engaged in childish activities.