expression, godan verb (-u)
the sins of the father shall be visited upon the son
Proverb meaning that children suffer the consequences of their parents' misdeeds. The verb 報う (むくう) here means 'to be repaid' or 'to be visited upon', often in a negative sense.
親の因果が子に報うというが、彼の苦労は父親の借金のせいだった。
They say the sins of the father are visited upon the son, and his hardships were due to his father's debts.