The man at the American Embassy tells Amir,

"It's a dangerous business, making promises to kids".

When Amir finally finds Sohrab and at great physical cost secures his release from Assef, he resolves to adopt the child and take him back with him to America.  First, though, Amir wants to get Sohrab's consent, and so he asks the boy if he would like to come with him.  Having been betrayed so many times before, Sohrab is hesitant, and expresses his fears that Amir might tire of him, and that he might have to go back to an orphanage.  Amir promises Sohrab that he will never let that happen, and Sohrab finally agrees to come with him to America.

Amir then tries to go through the proper channels to bring the boy home from Afghanistan, but finds that it will be much harder to do than he had anticipated.  When he goes to see Raymond Andrews at the U.S. Embassy in Islamabad, the official advises him to give up his petition to adopt Sohrab.  If Amir insists on going ahead to achieve his objective, Mr. Andrews warns that he will be met by obstacles which will be next to impossible to overcome.  As an example, Mr. Andrews tells Amir that he will have to prove that Sohrab is an orphan, which cannot actually be done because there are no death certificates for his parents.  As he angrily gets up to leave, Amir asks Mr. Andrews if he has any children, and the official counters with a question of his own.  He asks Amir,

"Have you promised this child you'll take him with you?"

When Amir responds, "What if I have?", Mr. Andrews shakes his head and says,

"It's a dangerous business, making promises to kids" (Chapter 24).