Your logic is flawed. Even if we reduced births to 10% of current rates. Those children would need more parental support for longer. As that generation would be more dependent on parental and family bonding due to lack of a same aged community to learn and grow with.

We are a species evolved to have very, very dependent young, rather than most other mammals. This presented up with advantages in the predator / prey fight that is evolution. But it also left our young depended on tribal societies to survive.

Parental leave is just the modern capitalistic equivalent of the tribe coming together to raise its young. It is the recent historic lack of it in many societies and post-industrial revolution that is odd. Not the return.

You as a non parent will eventually need these children to learn to manage the society you live in. Just because you choose to be child free yourself. Does not mean you will not depend on them as adults as you age. As you age you will need educated doctors nurses and Bin men to ensure your life is liveable. Those adults are the very children you think are not your responsibility now.

But unless you are a hermit living entirely on the milk of your own land. (if so you are already not funding this).

Then yes, you and all of us are involved in raising the future population.