The passage is significant on many levels including, as other educators have noted, that it represents the first sign of what will hopefully be a bond between Amir and Sohrab and that Amir has been able to break through to Sohrab through their shared activity of flying the kite. When the reader first is introduced to Sohrab, he is wearing heavy makeup that underscores his role as Assef’s captive sex slave. Not surprisingly, the boy is in despair and has nearly given up all hope before Amir’s arrival. That is why when after their escape Amir tells him that he might have to be placed in an orphanage while they work on getting to the United States, Sohrab attempts suicide. He knows what happened to him the last time he was placed in an orphanage.
Even though Amir and Soraya want Sohrab to know that he is safe living with them as their adopted son, the nightmare of his experiences in Afghanistan hangs over him, and he is unable to escape it. He is not a child as other western children are; his life up until now has been a series of horrific events, beginning with the murder of his parents and his being seized by Assef at the orphanage. When he finally smiles, even slightly, it is the first sign that perhaps he can overcome all that he has been through and learn to trust Amir and Soraya, to love them, and perhaps to begin to take pleasure in life.
The smile is also significant because it occurs when Amir and Sohrab are flying kites. This parallels the bond between Amir and Hassan, Sohrab’s father, as it was a favorite activity of theirs. There is a sense of nostalgia for Amir, and we can imagine Sohrab picturing his father flying kites with Amir when the two were boys. The smile is also significant because it parallels the frequent references to Hassan’s beautiful, guileless, and almost ever-present smile.