I've wondered if massive one time payments would be a solution. Like 100k for the first kid, 90k for the second, etc. Obvious moral hazard around having kids just for the payment, but if population decline is actually a big problem, it isn't necessarily worse.

Fixing the rest of what you mentioned is obviously a good idea too, but what better way to increase society's value on children than giving them a literal value?

ive seen similar things like no income tax if you have 3 kids. i think that give you slightly better alignment because you still want to be productive.