I believe "the suspenseful moment" that the question is referring to is meant to indicate the time that Ravi spends hiding from Raghu in the shed.  You are correct; it is a very suspenseful sequence.  Lots of writers include suspenseful moments.  Oftentimes, those moments are life-threatening experiences for the characters.  Desai's story does not use that kind of suspense.  Ravi is not in a life-threatening or dangerous situation, yet the hiding scene is very suspenseful, and it really draws readers into the conflict.  

The reader is held in suspense and is very interested in the conflict because the conflict is so familiar to readers.  We've all been kids before.  We've all played hide-and-seek.  We all know what the desire to win feels like.  Desai has provided readers with a situation that we are intimately familiar with.  When I play hide-and-seek with my own little kids, I can see the suspense on their faces when I come looking for them (and conveniently don't see them).  Seeing my kids makes me remember those feelings from when I was a kid.  Desai's story does that too.  Readers practically read that section of the story while holding their breath, because we don't want to signal Raghu any more than Ravi does.  

From there, Desai continues to build the suspense by describing the dark, spooky hiding place that Ravi has chosen.  It's dark, unfamiliar, and loaded with creepy organisms.  

But the shed smelled of rats, anthills, dust, and spider webs.

Most people have experienced being in a place like that before, and most people don't like the feeling.  So again, the story keeps the interest of readers by continuing to be familiar.  

In "Games at Twilight," how does suspense build interest in the final scene?

"Games at Twilight" is a wonderful story, and the suspense that Desai builds within the story is a huge reason as for why the story is so good and motivates young readers to finish the story. The story is shaped around an already somewhat suspenseful game. Hide and seek can be a nerve-wracking game, and most readers are likely familiar with the anxious feelings present when waiting to be found. Ravi has these feelings, and they are intensified due to the seeker being Raghu who is not known for treating the little kids very nicely. Ravi is genuinely afraid of Raghu and does not want to be found.

Once it is clear to Ravi that his hiding spot is a good one, he begins having visions of victory and grandeur. He is imagining all of the potential praises being heaped on him after he makes it back to the veranda. His excitement is palpable, and readers find themselves rooting for Ravi to win. We see his dedication to the hiding spot and his excitement at winning, yet we don't know if he will actually be victorious. This is a classic way to build suspense, and it has proven especially effective in a lot of sports movies. Audiences root for the hero, but we also realize that losing is a real possibility.

Ravi dashes to the den to claim his victory, and all of that suspense is released in the most disheartening fashion. The other kids have forgotten all about Ravi and have moved on to a different game. Nobody even thinks of congratulating him on hiding so well for so long.