Why does a minor fast if he kills someone else?

The expiation for unintentional killing is the freeing of a slave. If one cannot find a slave, then it is fasting for two consecutive months. The majority of scholars hold that expiation is obligatory for a child who kills, and it should be paid from his wealth. If he does not find wealth or a slave, then according to the Shafi'is, he is permitted to fast after the age of discernment, or according to the Malikis, the fasting is postponed until he reaches puberty. The Hanafis and the Permanent Committee are of the view that expiation is not obligatory for a child at all, as the pen has been lifted from him.