There are some interesting statistics in here. Of course, following these blindly ignores the causal vs correlative rule. Let's look.
Specifically, 86 percent of young people who got married before having kids are among the middle or top third of earners, while just 53 percent who put childbearing first have incomes in the middle or top third.
"Even millennials from low-income families are more likely to flourish if they married before having children: 71 percent who married before having children made it into the middle or higher end of the income distribution by the time they are age 28-to-34," report Wang and Wilcox. "By comparison, only 41 percent of millennials from lower-income families who had children first made it into the middle or higher end of the distribution when they reached ages 28-to-34."
This one is pretty strong.Wang and Wilcox's findings support the idea of a "success sequence," which was first introduced by Ron Haskins and Isabel Sawhill of the Brookings Institution in 2009. It says that the path to economic success and away from poverty is to do things in order: 1) Earn at least a high school diploma, 2) get a full-time job, and 3) marry before having kids.
Analysis:"Only three percent of millennials who followed all three steps, in sequence, are poor by the time they reach their late twenties or early thirties," Wang and Wilcox report. On the flip side, more than half of millennials who didn't follow the sequence are in poverty.
Not being married doesn't mean you don't have a supportive partner (I mean financially mainly). But being married seems to substantially increase those odds. Not because of the act of marriage but because of what tends to align when you do decide to wed. Marriage may also be correlated with a level of personal responsibility. Again, not the marriage itself. But there is a message here of course - it just probably shouldn't be taken literally.