Anecdotally, I know 4 or 5 couples who had kids and a mortgage before age 30 in the 2000's, probably two of them with only one income, the others with ~1.5 incomes. Not that your overall point is wrong, but depending on your location and education level it is completely financially feasible to purchase a home and afford kids on one income.
Within three years of college, I could probably buy a house on my own in Pittsburgh or many other areas in America's vast middle, even putting 20% down.
Heck, my friend bought a house in Seattle within six months of graduating. He's leveraged as hell, but has a job at Amazon and is renting rooms to friends.
