Also stated in the Abhidharmakosha-shastra is that some children may suffer the effect of seriously negative karma that their parents accumulated. If children can suffer the consequences of their parents’ negative karma, is this not contradictory to the Buddhist teaching that one reaps what one sows and that no one can assume others’ karma?
The Abhidharmakosha-shastra explains that these children themselves already have certain negative karma. Due to the close relationship between the parents and their children, the ripening of the children’s negative karma may be expedited by the extremely evil karma the parents committed.
~ Luminous Wisdom Book Series 1: On Cause and Effect