Most of the major themes of the novel find their way into the image of Amir and Hassan flying kites. Don't believe us? Here we go! First off, when Amir later tries to remember something happy, he pictures himself and Hassan flying kites. At first, there's such freedom and innocence in the activity for Amir and Hassan. However, the kites also become reminders of how Amir betrayed Hassan – abandoning Hassan to the nefarious Assef. We can go on. Kite fighting also represents, to Amir, a way to win his father's love. In fact, he does, though only briefly. Finally, when Amir and Sohrab fly kites at the very end of the novel, the kites allows Amir to return to the past without intense guilt. They're almost redemptive, mnemonic (something that assists your memory) images by the end of the novel. Of course, Hosseini refuses to definitively answer the question of Amir's redemption. So perhaps it makes the most sense to say the kites hold the possibility of redemption.
In any event, we do think they're fabulous images: violent, glass-sheathed strings attached to something light, something free. How's that for an image which contains both the tenderness and cruelty of the novel?