Who are the protagonist and antagonist?
The protagonists are both Yolonda and her brother, Andrew because we can identify with them trying to grow up in the middle of peer pressure, acceptance by others, and dangers that confront young people everywhere today.
I would say the antagonist is society itself as seen in the drug dealers who give Andrew cocaine, the boys who destroy Andrew's harmonica, the violence Yolonda witnesses at school when a boy is shot, and the cruelty of the kids who make fun of Yolonda's size. This part of society exists everywhere, in large cities and small towns, and it is these parts of society that children must face on a daily basis. This is what Yolonda and Andrew must struggle against in order to survive.