How far should adult children help their parents?

Many people would say right away that parents are responsible for their children, and they should provide as much as their capabilities allow. However, what about children? Are they expected to return the favor? I mean chances are many parents sacrificed, worked hard, and tried not to deny their children materials, trips, and experiences.

So, if parents are in need of some financial assistance (assuming they were good and responsible people), should their adult children help them? Some would say a definite yes, and others would say no. I know in the U.S. and some other nations, the government offers a social security or related programs. So parents don't need to depend on their children for everything. This doesn't work for other nations. Many parents live with their children, and depend on them for financial assistance.

Just how much should parents depend on their children? Should adult children comply even if they are not capable (because of all the sacrifices their parents went through for them?)? These are tough questions. I think the most important is trying to find a balance. This should be discussed with your own parents, and then try to come up with a reasonable solution.