Do grown children have a special duty to support or assist their parents?

Pro: The special relationship between parents and children entails special responsibilities for both parties.

Pro: Parents make an investment in the well-being of their children, and children have a debt to repay. Children should care for their parents as much as their parents have cared for them.

Con: Children did not ask to be born, and what care their parents gave them, the parents gave willingly and without an expectation of a return on investment.