Just to clarify one issue...
In cases where a child is paid Social Security benefits because one parent died, legally speaking, that money belongs to the child even when the child is still a minor and thus the SSA sends the payment to the surviving parent. The parent receiving the money on behalf of the child is acting as a fiduciary and must be VERY careful in how they preserve the CHILD's asset.
I'm an attorney and my secretary is in this situation -- her husband died a few years ago and their (now) 13 year old daughter gets his SSA benefits. My secretary wanted to tie the money up in a trust with limits on how it can be spent (for education) so the child doesn't get a windfall at age 18, but legally, she may not do that. If the SSA overpays my secretary then, under the law, they've overpaid the child. The mother is just the agent.
So, in this situation where the SSA overpays a custodial parent (by, for example, continuing to send payment after the child is 18 and should no longer get them; or if the child died before reaching age 18),legally the SSA overpaid the child because the money belonged to the child and that's why the IRS is coming after the (now, adult) children. Any adult child in this situation may have a cause of action against their parent (slim chance of that, but maybe if the parent knew of the overpayment).
Fun times.