You only need kids if your society is in a position where those with the wealth to afford children are not having them. Japan certainly has that problem, curren

You only need kids if your society is in a position where those with the wealth to afford children are not having them. Japan certainly has that problem, currently, the US does not. If you are in the Japanese situation, I would still argue opening up immigration is almost certainly cheaper an option than subsidizing child rearing, but we are no where near any problems stateside involving population replacement, and if we did, again, we can open our borders much more before turning to child subsidy.