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.

"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.