Both child-haves and child-have-nots pay SS taxes, but only the child-haves perform uncompensated labor by raising future taxpayers. Contributions are there, but they are not equal.
The fact that SS has become pay-as-you go is the government's fault
If it were not a pay-as-you-go system, the money would have to be invested somewhere, and investments won't be worth much unless there is a vibrant underlying economy, with labor and consumers spending - and those future workers and consumers are today's children.