how does sohrab respond to life with amir and soraya?

Eventually, Amir did bring Sohrab home with him to San Francisco. We discover that Amir has been narrating the story in 2002, seven months after they arrived. Sohrab had not spoken a single word since then. He showed no interest in the books Soraya had bought him or any activity they suggested. They did not tell the Taheris the story of why exactly they were adopting Sohrab or how Amir had gotten injured. One day, General Taheri said, "People will ask. They will want to know why there is a Hazara boy living with our daughter. What do I tell them?" Amir, angered, told the general that Sohrab was the son of his illegitimate half-brother and told him never to call him a "Hazara boy" in front of him again.

The political landscape had changed in the interim since Amir and Sohrab arrived home. The Twin Towers had fallen in New York City and The United States had bombed Afghanistan, compounding the damage done by decades of fighting. Amir found it strange to hear non-Afghan Americans discussing the cities of his childhood. He and Soraya began to get involved on Afghanistan's behalf, trying to restore a hospital on the Pakistani border. Amir had kept his promise to pray after Sohrab had survived his suicide attempt.

Amir explains that four days earlier, a miracle happened. He and Soraya took Sohrab to an Afghan picnic in the park, along with Khanum Taheri. General Taheri was not there because he had finally gotten his wish; he had been offered a post in the Afghanistan ministry. By now, people had gotten used to Sohrab's silence and even Soraya could not bear trying to engage him anymore. Only Amir kept trying. Suddenly, Amir noticed kites flying over the park. He bought one and brought it to Sohrab. He told him that Hassan was the best kite runner he had ever known and asked Sohrab to fly the kite with him. Sohrab remained silent, but Amir knew what to do; he ran as fast as he could to launch the kite. As he stared up at it, he noticed that Sohrab had followed him and handed him the string. Sohrab soon gave it back to him. They stood in silence once more until they noticed a green kite closing in on theirs. When the kite came close enough, Amir performed Hassan's favorite kite-fighting trick, "the old lift-and-dive" as Sohrab watched, mesmerized. The green kite fell out of the air. When Amir looked down at Sohrab, he witnessed a half-smile steal over Sohrab's face. He asked, "Do you want me to run that kite for you?" Sohrab nodded, and Amir told him, "For you, a thousand times over." Amir ran among the children, after the kite.