Who knew utterly destroying cities and replacing them with gated communities with no accommodations for children whatsoever, and borderline criminalizing any activity which isn't closely supervised would have knock-on effects.
There are many types of activities which, while not criminalized yet, are “anti-social” in certain environments and can cost you your job.
They are also all experiencing pressure to be criminalized and in certain places are already criminalized or otherwise regulated in a way that is harmful to individual liberty for a perceived gain in safety.
Lastly, I’ll add that cost of insurance, general ability to be insured, and the litigious nature of the USA apply a great deal of pressure to limit our ability to enrich our lives with risk.
Edit: what I want to say is that mobility does not create community and stability. I see this in Germany often: school system does not create community either. A child must go through at least couple schools. So the friends get lost and strong friendship does not happen in the last school.
US birth rates started dropping off not a generation later.
That factoid doesn't mean much on its own.
The transition away from communities where kids had autonomy, regualr access to adult-free spaces and also easy access to a wide variety of adults - the loss of all that massively increased parenting time and resources, from a few hours per week to 24/7 adulting.
Modern young parents now how to replace many diverse and experienced adults and impossibly simulate the autonomous and independent spaces where kids learned interpersonal and problem solving skills.
The closer we got to this, the less people wanted to have kids.
Blaming the depression and word war is a bit of a stretch.