This is a very important prompt to consider for both Hassan and Amir, as Amir begins this novel by recording the precise moment of his childhood that determined what his adult existence would be like:
I became what I am today at the age of twelve, on a frigid overcast day in the winter of 1975. I remember the precise moment...
Just as Amir's future as an adult is shaped by his decision not to help Hassan in his time of need, so Hassan's future is shaped by his experience of being racially abused and physically violated because of his ethnicity. It is this, as Rahim Khan reveals to Amir in Chapter 17, that results in Hassan's execution, as it is because he is a Hazara that Taliban officials throw him out of Rahim Khan's house:
Soon after I took my leave, a rumour spread that a Hazara family was living in a big house in Wazir Akbar Khan, or so the Taliban claim. A pair of Talib officials came and interrogated Hassan.
Just as Assef abused and violated Hassan in his childhood because of his ethnic identity as a Hazara, so too does Hassan face the same persecution in his adult years. Hassan's experiences of racial discrimination in his childhood shape his future, as this is the same treatment he experiences in his adult years.
However, it is also possible to argue that Hassan manages to remain untouched by the experiences of childhood. For example, Amir remains dogged by the past, which is personified as a monster trying to "claw back" into his life as an adult. Hassan, however, in spite of being the victim of a violent rape, seems to be able to grow up to marry and have children and be a faithful and kind individual. He, unlike Amir, is able to live a meaningful life in spite of the past. This could be one way of contrasting Amir from Hassan, as both have very different relationships with the past.