The decline in birthrates is often attributed to the cost of raising children. In the premodern world children went to work as early as six or eight, and thus constituted an economic benefit to the family; in the modern world they don't start working until they're teenagers, later if they attend college, constituting a huge upfront cost without much return for decades, if ever. "Surely this explains why birthrates are decreasing." It does not. Various countries have experimented with various degrees of income support for parenthood: paid maternity/paternity leave, childcare subsidies, direct cash payments. The effect on the birthrate of all these programs appears to be approximately zero.
I know this isn't everything that's going on here but whenever I see this I think "would you base this decision on a child-raising benefit that was legislated last year? That may or may not continue, either actually or effectively?" Can be an extent to which you don't want to trust any child welfare program until it's lasted multiple generations.
See a bit of the "redistribution vs predistribution" arguments, give people money or try to arrange the economy such that their wages are higher. Any redistribution in the current moment is going to feel very transient. Predistribution too, although perhaps we can be fooled into think this represents some sort of "natural" income that will last.
