Parents choose to have children.
Children do not choose to be born.
This means that children owe their parents nothing in exchange for taking care of them before they are capable of taking care of themselves. It was the parents' actions which are responsible for the state of the child's infirmary (relative to adult capabilities), therefore it is their responsibility to correct.
Everything that parents do to bring their child into adulthood is simply the fulfillment of a obligation they incurred when they created a helpless and dependant child.
Do you expect your bank to go out of their way to thank you for paying your mortgage on time every month?