How does Desai deal with the theme of oppression in "Games at Twilght"?
That is an interesting question, because oppression isn't a super-obvious theme that I would have come up with for that story. There isn't any blatant cruelty or horrific acts of oppression going on; instead, there are instances of childhood cruelty that results in the ostracization, and I suppose, oppression of childhood spirits.
Ravi is the victim of oppression in this story. He starts off the story as an excited, hopeful, involved child, and in the end we see his spirit crushed and oppressed by "his terrible sense of insignificance." Where before this moment he had been in the old shed, imagining defeating Raghu, a moment he felt would be "thrilling beyond all imagination." He was excited, anticipating the defeat of the bully Raghu, and in the throes of full, unabashed childhood imagination and happiness. But then, as he exits the shed too late to be the winner of the game, and realizes that they all had not even noticed his absence, his spirit is oppressed. We see him lose a bit of that childhood freedom and become weighed down and oppressed by the rather grown-up and maturing knowledge that he might not matter as much as he thinks he does.
The other mentionable aspect of oppression in the story is the character of Raghu, who, with his bullying, whining and random viciousness, strikes a bit of fear into the hearts of his playmates. Their sense of elation and freedom is oppressed by his mere presence.
I hope that those thoughts help a bit; it's an interesting question. Good luck!