why are the boys and fathers so affected by the gift baba gives to hassan?

Baba usually gets Hassan something special, like a Clint Eastwood cowboy hat or train set. This year, Baba finds Dr. Kumar, from New Delhi. THe doctor will perform surgery on Hassan's harelip. This is an especially expensive gift. It also tells us that although Hassan is a Hazara, Baba still respects him. Baba respects Hassan's courage and strength which he finds lacking in Amir.

In addition to what Aslan said, later in the book we do find out that Hassan is Baba's son. So in that case Baba just shows what a father would do to cure his son.

sorry I forgot to read it says that the answer has to be from Chapter 5, how do u delete an answer??