Where has this been shown to work?
By and large, the nations with more childcare support, more protections for pregnant women, etc have lower birthrates than those that don't.
For example, if we look here: https://en.wikipedia.org/wiki/List_of_sovereign_states_and_d..., then America seems to be the developed country with the highest birth rate despite having little of the social policies you mention.
In fact, based on that chart, it would seem the opposite is true. The less social safety net, the more kids. This makes intuitive sense since if government isn't taking care of you, you'll need children to.
Give poor women education and access to those, and even poorer countries will see similar declines in birth rate.
I think humanity’s growth was dependent on women not having a say in the matter. All the situations I see where women have gained the ability to easily choose whether or not to have kids lead to lower birth rates.
Seeing new role models who had interesting lives, and especially learning that it was possible to withstand pressure from grandparents to have children seemed to be more important than mere availability of contraceptives or education.
IIRC there was a similar effect in Bangladesh, but it was harder to track since TV rolled out more quickly there.
One wrinkle is the gap between how many children women say they want when surveyed (about 2.5 in most western countries) and how many they end up having on average (fewer).
It could be that the surveys are asking the wrong questions, or that for some people they just never get the circumstances they want.
As far as I know that gap has never been conclusively explained. Hypotheses abound, of course.
That's because they also have more public poverty and old-age support; which reduce the incentive for large families as old age and disability “insurance”.
Which on its own is a good thing, but if you want to encourage births anyway, your public support for parenting has to offset the effect that has on incentives to have children, which is a very bif effect. Nations don't do that because they don't think its an important-enough public need to warrant that approach.
We hesitate at being dependent on others or having others help us. In the us, no matter your political side, the idea of finding meaning only through service to others is not only in short supply it's actively demonized.
For now, it's easier to kick the can down the road.
The other kind of trying is when you put vigorous effort into making it easier to have children. Dramatically ramp up childcare support. Strongly enforce anti-discrimination laws, particularly in the case of discrimination against mothers. Forbid employers from requiring more than 40h of work per week under certain (very high) compensation thresholds. Provide direct payments to parents that substantially offset the costs of additional children. Align housing policy with the need for larger dwellings for larger families, but still with decent commutes. Etc.