Symbolism, Imagery, Allegory
There are two things that really fly in the novel: kites and birds. And flight, in literature, usually represents things like freedom or escape. So when Harish leaves to fly his kite as his mother works in the brothel, he's escaping from something that he wants to leave behind:
But in the evening, it is harder to pretend. As soon as dark falls, the bigger ones go up to the roof. They fly homemade paper kites until they are too tired to stand, daring to come down to sleep only late at night after the men have finally gone. (96.Pretending.11)
So the flight of a kite for Harish is a way of escaping his harsh reality. The symbol is obvious enough that we're almost prepared for what is on the business card the first American leaves Lakshmi:
It is full of American words I cannot read, and in the center is a drawing of a bird in flight. (137.AStrangeCustomer.28)
And as we follow this image, a bird in flight—freedom—throughout the rest of the novel, we too find ourselves full of hope that Lakshmi will fly free.