Parents who have OTD children often complain that they were not good parents. They are then brought back to reality when confronted with the successes of their other children. While there are dysfunctional homes and there are parents who are failures in the parenting department, most parents are adequate or better. (I learned this at MASK meetings.)
The fact is that children are not identical, and each one needs a parenting style that is molded to fit the individual. Yet, many parents try to mold the child to fit the parenting style, and this can become a problem. This problem is rampant in chinuch when all children are expected to respond identically to rules, teaching styles, curricula, and discipline styles. The good rebbe knows how to manage a classroom with inequality (as in ???? ???? ?? ?? ????).
When a parent misapplies a parenting strategy to a child where it backfires, we have the making of problems, including OTD. These errors are sometimes neglectful, rarely intentional. Focusing on the parent, as in laying blame, is futile. Past actions cannot be changed, and expecting that to be the only cause will divert attention from many other possible factors. There is much that parents can do to help the situation of an OTD child, but the blame stuff does not work.
As to the matter of the Avos being held responsible for the sins of their children, we must place this in the context of how HKB”H deals with tzaddikim ???? ?????, held up to a higher standard than anyone else.