The climax of "Games at Twilight" occurs when Ravi runs out of his hiding spot and shouts "den" to claim his victory.  

The denouement, or falling action, of the story is when the kids do not give Ravi credit for winning the game.  They completely forgot about Ravi and moved on to playing another game.  Ravi is near complete devastation, and the falling action moves toward the story's final conclusion.  That conclusion is Ravi's realization of just how insignificant he still is.  

He lay down full length on the damp grass, crushing his face into it, no longer crying, silenced by a terrible sense of his insignificance.

That realization ties in with a theme of the story.  The theme would be the alienation of the individual.  Ravi feels alone and inferior throughout most of the story.  Ravi is not a leader, and he feels inferior against the bully Raghu. Ravi believes that winning the game of hide-and-seek will help earn him recognition and popularity.  

To defeat Raghu—that hirsute, hoarse-voiced football champion—and to be the winner in a circle of older, bigger, luckier children—that would be thrilling beyond imagination. He hugged his knees together and smiled to himself almost shyly at the thought of so much victory, such laurels.

Unfortunately, nobody believes that Ravi won the game, and he is relegated to being just as insignificant and alone as he was before.