It's not clear exactly what the number is, but if one observes individuals who manage to climb out of the low and middle classes and accrue a certain amount of wealth (somewhere in the ballpark of $600k-$1m net worth and up, maybe), pretty consistently not long after that achievement they've settled down and started a family.

I think for many the desire is there, but sufficient de-risking is required for them to be comfortable with acting upon it.

$600,000 net worth is nothing these days, I’m worth about that much after saving for 7 years and can’t even afford the mortgage for a $300,000 house, even if I put 20% down.

Investments are so much better at earning money than working for wages, in my case the amount of retirement savings I have after 7 years is larger than my cumulative earnings during the same period, and I’ve been saving about 40% of my gross income. Part of my net worth is ESOP equity that I can’t monetize in any way so that’s part of the reason why my net worth is higher than my earnings over the same period.

I think there's just not enough money in the county to induce more babies. The cost would be a shock. Anyone wealthy enough to shoulder the cost would fight so hard against it, it would never stand a chance. IMO the number is probably something like $10k per year per kid. Foster Care pays somewhere between 8k-12k.