At a deeper level it is about delinquency, war and human nature. Try to sum up what the story says about human nature in general.
At its most basic, "The Destructors" can be read as an observation of man's inhumanity to man. Trevor, the gang's leader on their project of destroying Old Misery's house, is the son of an architect who has come down in society rather abruptly after being let go from his job. Consequently, Trevor channels his anger into destroying a valued symbol of the world that has treated his family so badly, a house designed by Sir Christopher Wren.
The fact that the boys are so quick so follow Trevor and discard Blackie as their leader suggests that loyalty among these boys is not valued. And the narrator mentions that Mike had been told at the age of nine, “If you don’t shut your mouth . . . you’ll get a frog down it.” Brutality toward others is commonplace in these boys' milieu.
The boys don't think about what the destruction of the house will do to Old Misery (or the disrespectfulness of their nickname for Mr. Thomas). Though the elderly man had shown them some kindness by giving them sweets, they are eager to destroy his house. They give no thought to his humanity or vulnerability as a senior citizen.
In the story's final scene, there is another example of man's inhumanity to man; the lorry driver whose truck ultimately pulls down Old Misery's house is unable to contain his laughter at the sight of the house reduced to rubble, even when Old Misery exclaims, “How dare you laugh . . . It was my house. My house.”
Because the members of the firm that sacked Trevor's father and the lorry driver are adults, Greene reminds us that it is not just children who are cruel to one another.
"The Destructors," by Graham Greene, is a haunting short story in which a gang of boys destroy a beautifully made house. What is so disturbing about this story is the time, effort, coordination, and teamwork that is used to destroy Old Misery's house, one of the few grand houses left standing after the war, presumably WW2.
But the story is not about greed, revenge, or anger. Instead it is purely about delinquency--destruction for destruction's sake within a society that is accustomed to such things being destroyed--post world war England.
The boys are merely following suit. Just like the adults before them in war, they are using their talents to destroy rather than create. It seems as if Greene is showing man's potential and choice to do either. Creation and destruction require hard work, and people will choose one or the other depending on their surroundings, morality, and upbringing.