An interesting argument I saw recently is that car seat regulations are not an insignificant part of the fertility crisis. I’m going from memory here, but the idea was that by making parents use booster seats for children, you’re strongly discouraging a 3rd child, since you can’t do 3-across booster seats in most cars, and getting a bigger car with a 3rd row is taking on an extra expense that some of them can’t afford.
You can say “ok, have your 3rd kid once your older kids age out of the booster seats”, but people are getting married at older and older ages, and a lot of women are getting outside of their fertility window by that point.
@dave maybe biggest child on front seat, parent on middle seat in the back. isn't comfy though ;)