«وَمِنْهُ أَيْ مِنْ جُمْلَةِ هَذَا النَّوْعِ رِوَايَةُ الآبَاءِ عَنِ الأَبْنَاءِ»
“Among the instances of this kind is fathers narrating from sons.”
Children ordinarily learn from their parents, but hadith transmission can also run in the other direction: a father may receive a report from his son. This is a more specific example of senior-to-junior narration, since the family relationship normally establishes an age difference.
Example: A father hears a particular isnād from his son, who obtained it independently from another teacher. The son is the father's source for that report; kinship and the direction of scholarly reception are not in conflict.