Anita Desai uses a combination of direct and indirect characterization to develop Ravi.
There is quite a bit of direct characterization happening with Ravi in this story. Readers are told many specifics about his build and his thoughts. For example, we are told that Ravi is short when Desai talks about his short legs being the cause of his slow running ability.
Desai uses indirect characterization early on for Ravi as well. Probably my favorite line about him is the following line.
Ravi heard the whistling and picked his nose in a panic, trying to find comfort by burrowing the finger deep—deep into that soft tunnel.
Readers are specifically told that Ravi is in a panic and picking his nose to find comfort, but within that sentence is a lot of other information about Ravi. He's not a very confident kid. The kids are playing hide-and-seek, yet Ravi is terrified. He also finds comfort in picking his nose. This tells readers that Ravi is likely that "weird" kid who still picks his nose at an entirely too-old age. He's probably not well-liked, and he doesn't have a lot of friends. Those suspicions are confirmed by the end of the story when readers see that nobody is willing to admit that Ravi won the game. In fact, nobody even remembers that Ravi was playing at all.