Even if one tries to apply first principles it's not something that can be derived easily to hold your statement as fact.
The birth rate is declining faster than expected across the whole world. There aren’t going to be enough young migrants to go around and keep pumping up the numbers.
Probably free daycare and relaxing immigration would be best to increase population
France has a subsidy program for kids. It's not helping much. Current fertility rate is 1.85 (2.1 is breakeven).
The only thing that seems to work is a religion that keeps women home pumping out babies and taking care of them. Islam and Haredi Judaism do that. There's a Christian "quiverfull" movement in the US, but it's not big enough to matter.[1]
The issue is non-market housing used to be roughly 30% of the renting market, applying downward pressure on rent prices and thus, house prices. It's now less than 20%, with 95% being 'HLMs' (and a big part of those were from 'loi Pinel' that ended this year). We need to get back to a high percentage of non-market housing.
My father used to be the co-director of a 'chantier d'insertion' where he was teaching basic woodworking/painting/construction/DYI and also artistic skills to people (mostly men) outside of the workforce (from the 16yo dropout to the 54yo ex-farmer), and they did own a few buildings they restored, to help house everyone (they also had people teaching mechanics, electric, plumbing, gardening btw). The local city council changed it's political side, the initiative was shut down and the non-market houses bidded on. The GDP of our city that year probably skyrocketed.
PS: not on the subject: he still had time to clean up an ex-slaughterhouse with his guys, and organize an art exposition inside, with 'mort aux vaches' tagged outside with blood-looking paint, which, considering the new mayor was from a military family, had a not subtle double meaning.
Industrialized and highly educated populations will not go back to 2.1 and higher, it just doesn't work like that in the current social environment.
paid for by the people who don't have kids
not very different than just giving out cash or tax credits
Funnily enough, https://en.wikipedia.org/wiki/Mother_Heroine was reinstated in 2022. Russia's current birthrate is ~1.5. Ukraine has something similar as well, they're doing quite poorly, even before their war at ~1.3.
My radical take on all this birthrate stuff is that the single most effective way to boost the birthrate is to entice boredom in any way you can. The internet was a great invention, but the great cost was our attention. It's likely out of the bag that we can't revert to a minimally networked world though. I would (and do) certainly fight against attempts to ruin the internet myself.