We would be even better off subsidizing parents staying home with their own children. Unfortunately most subsidies have proven ineffective at nudging up birth rates.

In an emotional development sort of way: maybe. Subsidized childcare however provides two jobs to the economy for the price of one and every single person worried about birth rates is either a white supremacist or the sort of emotionless economist that 2:1 is appealing to.

Those subsidies tend to be €X00 per month. I am not aware of any scheme that even attempted to replace 80% of forfeited wages. A subsidy that ends up with you having to move impoverish yourself is not going to have the desired effect.

Why would that be better? I think you'd miss out on economies of scale and end up paying more.

No, we wouldn’t. This subsidy directly benefits the survival rate of children while universal basic income is too broad. healthcare is more affordable than UBI.