I think the best advice to having kids young is to lower your expectations. The only reason people ‘cannot’ have children young is because they want a specific kind of life for themselves and their kids that is incompatible with that.

The difference likely there is in the ‘40s you were seeing improvement after the Great Depression and employment during the WWII, followed by the postwar boom. Whereas the past two generations have seen precarity increase while living standards falter if not drop compared to their parents’ generation. So they are striving to recreate what they once experienced in their childhood, what was once there, yet may never appear once more.

Also the entirety of society including their families emphasizing the importance of higher education, good careers, etc. even as the latter is harder to achieve and the former becomes increasingly devalued, and pricy.