How is the kite flying episode in the first third of The Kite Runner different than the one in the last third?

Hosseini  constructs the kite-flying episode in Chapter 7
to further develop the relationship between Amir and Hassan.  Though Amir is nervous,
Hassan continually encourages him, and the competition ultimately ends with Amir's
victory.  When Hassan takes the blue kite to run it for Amir in celebration, Amir's
focus shifts to his thoughts of Baba, whom he has finally made
proud. 

During this time, Amir loses track of Hassan, and
the scene that follows--in which Hassan is raped by Assef--is one of the most poignant
and disturbing in the novel.  For, Amir, a witness to this horrible act, is unable to
act in Hassan's defense.  Afterwards, Hassan returns home, traumatized both physically
and emotionally, holding the blue kite.  For the rest of the novel, Amir's guilt,
coupled with Hassan's presence and failure to ever mention the situation again, proves
to be too much for Amir; he ultimately constructs and executes a plan to drive Ali and
Hassan from Baba's home.   This episode serves as a reminder to Amir, and to readers, of
Hassan's unrivaled love for and commitment to Amir; Amir's failure to reciprocate is an
issue with which he is left to deal with for the rest of his
life. 

In Chapter 25, the final chapter in the novel, an
adult Amir buys Sohrab a kite and takes him out to run it.  After a tumultuous year in
which Sohrab refused to speak and even tried to commit suicide to avoid being placed in
an orphanage, this kite-running experience evokes Sohrab's first smile in Amir's
presence.  As Sohrab is Hassan's son, and as Amir has gone through many extraordinarily
difficult and trying situations with the child, this smile is what Amir refers to as a
"small, wondrous thing."  The novel closes with Sohrab and Amir running kites together
with the hope that both will move forward together from the difficulties that each has
endured.