I don't agree with the GP at all, but I think it was pretty much established that money is not the primary reason people have less children. Perhaps obvious example, in general it's the rich countries that have problems with replacement rate and the poor countries pick up the slack (and not the other way around). For a more direct example, the populist government in my country started giving out money, no strings attached, to people with children, and the fertility didn't change at all (even declined a bit). So I think it's pretty clear we need other solution if we want to fix that.