Sarah Perry argues that children have been nationalized, have become property of the state and ceased to be the property of their parents, so have become a cost to their parents and a profit to the state, so parents decline to produce so many.
Makes sense, certainly part of the story, but not what I seem to observe, not the main story.
What I seem to see happening is that the major cost deterring people from children is not economic, but rather loss of female sexual autonomy. If a woman has children during her fertile years, then she is not longer able to respond promptly to a midnight booty call from Jeremy Meeks.
Your feelings differ from mine? Let us look at Augustan Rome.
The Augustan reforms made children the property of their parents, but the wife even less the property of her husband than in the modern west. Fertility continued to collapse, to levels that may well have been substantially lower than modern western levels.
On the other hand, the Pauline reforms, which were that a man and his wife were one person, and that person the husband, that the wife was part of the husband, did help substantially with fertility.
Further, I don’t think the nationalization of children is really separable from feminism. Women really cannot look after themselves. They will either attach to their fathers, their husbands, or Uncle Sam the big Pimp. Thus feminism, in practice, means that children become the children of Uncle Sam the big Pimp. If you denationalized children, women would spontaneously submit to patriarchy. Conversely, if you enforce patriarchy, the patriarchs will claim their children. To maximize fertility, need that form of patriarchy in which women attach to their husbands, rather than their fathers, and females are rationed out at only one wife per male, so that as many males as possible have incentive to attach to society, to work, and to invest in posterity.