> You may think this ought not be true, but as a matter of reality it is. Each generation carries the weight of the previous one through retirement.
To the extent that this is true, it is by choice.
> Is it just? I think so - but regardless of that, it is the agreement every child is born into.
"Agreement" presupposes the consent of each party. You cannot be entered into an "agreement" without your own participation in the act of agreeing.
Children cannot consent, therefore this is no "agreement" by definition.
What you have called an "agreement" is more appropriately referred to as a "duty." There is a very critical distinction between the two concepts which I will elaborate on in a moment.
> Somewhat, but it is rude to point that out.
What do manners have to do with anything?
What you're describing is the concept of duty. You're saying that by virtue of just being born, a child is obligated to care for his or her elders through retirement and that their personal choices are irrelevant.
In this case there is a very important question: "What are you going to do about it when the child says 'no'?"
You can either do nothing, which is a valid option, but it means that the entire concept and discussion was moot. You can invent "duties" all you want, but people ultimately get to decide how to live their own lives and there's nothing you can do about it.
Or, you can pass laws and use force in order to compel people to do certain things "for the good of society."
Which brings me to why I asked the question: "Are people who choose to be child-free parasites?"
That's a very important question because if a "society" depends on children in order to pay peoples' pensions and to take care of them when they are older, and that dependence is so fundamental that we consider people who choose not have children "parasites", and we obligate children to a duty to take care of elders ... then you've weakened the recognition of individual rights (at least reproductive rights and the right to travel / emigrate) to such an extent that you've opened the door to banning contraception, abortion and freedom of travel.