What is the ruling on someone who ran over a child with a car without seeing her, and her guardian waived the blood money (Diyyah)?

Whoever runs over a child with his car without seeing her is considered to have killed her by mistake, and two things are incumbent upon him: the blood money for the deceased, to be paid by the killer's 'Aqilah (male relatives on the father's side), and expiation. If the guardians of the deceased pardon the blood money, it is waived, but the expiation remains. The expiation is freeing a believing slave, and if one cannot find a slave, then fasting for two consecutive months. Allah Almighty says: "And it is not for a believer to kill a believer except by mistake. And whoever kills a believer by mistake - then, freeing a believing slave and a compensation (blood money) presented to his family, unless they give (it as) charity." (An-Nisa, verse 92).