What is meant by "a righteous child who supplicates for him"? And is it a condition for the child to be committed, or is the supplication mentioned in the Hadith the well-known supplication?

The phrase "a righteous child who supplicates for him" means that the deeds of the deceased are cut off except for three: an ongoing charity (sadaqah jariyah), knowledge from which others benefit, or a righteous child who supplicates for him. What is meant by a righteous child is a believing, upright child. The reason for restricting it to a child is to encourage children to be righteous and to supplicate for their parents. Furthermore, every good deed performed by the child, its reward reaches their parents. What is meant by supplication (du'a) is asking Allah for mercy and forgiveness for them.