The solution is probably buried in the reasons people use to not have children. The “costs” to raise a child can easily exceed a family’s abilities. In the US, maternity leave, if offered at work, only lasts the first few months. But the child’s need to be supervised 24/7 doesn’t end for maybe even a decade after that. (I don’t know the real timeframe, but suffice to say it’s years.) A family needs to find someone or company to watch their child(ren) for years. That alone is a prohibitive requirement. I think society could solve two problems with one here, but clearly not with current market factors. Society could subsidize child care - thus increasing employment, GDP (ultimately), and family formation.

This is just a hypothetical example.