Comparing what folks did 50 or 80 or 100 years ago to what folks do today is pretty much a waste of time.
Folks regularly had 5 - 7 kids back in the ‘50s and ‘60s? Let's take a look at a few example of the differences between then and now.
I was the third of four children, my wife the last of five. Our families were working/middle class. We owned modest cars. No vans or mini-vans. At best, a station wagon with five standard seats. So, how did our families fit 6 or 7 people in our cars? We just sat closer together! Oh, but wait. Couldn't do that in a modern sedan or a smallish station wagon. Not enough seat belts. And failure to have everyone belted in is a violation of law, drawing fines, and I guess even worse on multiple incidents. When she was a child, my wife rode in the “way back” of the family station wagon, often hanging out the rear window. Today, that’d likely bring arrest.
We all went to Catholic school. How did we manage? Easy. Our families put an envelope in the basket every week, went to Mass every week, and volunteered around the parish. Our pastors made sure our parents would be able to afford Catholic school for all of us. Even if it meant half price for kid #2 and free for the remainder.
Doesn't exist anymore.
A few years back, I sat on a local scholarship committee for Catholic schools. I read through folks’ financial statements and tax returns. Other than very, very well off families, no one could afford to send 5 - 7 kids through Catholic school. When elementary school runs $6K and high school (at the low end) $15K, five kids in school might mean $50K per year in tuition. Without uniforms, books (typically $1K per year in an academic high school), no less band or sports. Median household income in the United States is roughly $60K per year. Large, median Catholic families can't send their kids to Catholic schools.
Remember that according to Church teaching, use of Catholic schools by Catholic families is SUPPOSED to be normative. The only problem is that real, live, actual, large Catholic families are now shut out of Catholic schools. Unless they're rich.
When my wife was a child, it was seven folks in a three bedroom, one bathroom house. Such a family might draw the interest of “child welfare” authorities. You wouldn't even be able to rent an apartment, nowadays, for seven folks. Heck, even in 1966, when we first moved to Maryland and at first lived in an apartment, my parents had to search high and low for an apartment complex that would permit six people in three bedrooms.
Whether by actual legal requirement, or by true lack of affordability, or by strong social custom, it really is true that at least for Catholics, median-income folks, large families really are no longer affordable.
Some still manage to do it, but it is often by way of special circumstances, often because now such families are the exception, not the rule, and always by way of heroic virtue.
It's anachronistic to make the comparisons.
sitetest
How do they live without two incomes? Actually, they live cheaper, and they've found homeschooling cheaper even than public school, because they don't have to worry about the kids competing with or comparing themselves to other kids in clothes, toys, and other possessions. And transportation? When you don't have to shlep everybody back and forth to and from school and afterschool activities every day and half the night, it's just incredibly simpler.
One of the moms does do a certain amount of real estate sales from home. Another, web design. So creative. I admire them so much.