al-Salamu `Aleykum, A father killing his child gets two punishments, the first punishment in this life is that he has to pay Diyyah, in one narration a father killed his son so `Umar (ra) punished him by making him give away 100 camels, and he does not inherit his son or take any of his blood money. The second punishment is in the after-life, he goes to hell. And the ruler or Ameer or Caliph may increase the punishment as he sees fit, such as jail for life and so on...