Millennials still want kids, just not right now

Subsequent generations of women have largely followed their lead. There are no signs that most millennial mothers want to go back to the big families of the post-World War II era, for example. But, just like so-called Generation X, millennials have also made surprising choices of their own, some of which are just starting to show up in demographic data.

When and whether women have kids is a decision with serious economic consequences that affects their education and career trajectories. Boomer women tended to get married and have their first children by age 30. Those who opted for college or graduate school were far more likely to remain childless.

A Bureau of Labor Statistics study released last month of younger boomer women, those born from 1957 to 1964, showed that 70 percent became mothers by 30. By their late 40s, 83 percent of them were mothers, with an average of 2 children each.

Younger generations haven't been in such a rush to be parents. Generation X-and millennials even more so-are waiting longer to start families, especially over the last several years:

The birth rate for teenagers and women in their early 20s has dropped quickly in the last few years, and birth rates for older American women are going up.

Births by women over 40 are still relatively rare, but their birth rate has doubled since 1990.

As a general proposition, Americans still say they want kids. Since the 1930s, Gallup has been asking about "the ideal number of children for a family to have." In 1957, the average answer was 3.6. By 1977, it plummeted, to 2.6, but then the decline stopped. In 2013, the most recent survey, the average ideal number of children was also 2.6, and the most popular answer was 2 children, given by 48 percent of respondents. So we want children, only later.

But will Americans put forth the number of children they say they want? It's not clear if the rise in fertility by thirtysomethings and fortysomethings is enough to make up for significantly fewer births among teens and young adults. Millennials may eventually get around to having the same number of children that their mothers did, but they'll need to do so at much later ages.

One factor is marriage. Millennials are getting married later than their parents did. That doesn't necessarily mean they're going to abandon the institution entirely, especially if they're having kids. In 1960, almost nine in every 10 children were growing up in a home with two married parents. That fell rapidly in the 1970s and continued to fall at a slower pace in subsequent decades. By 2012, 64 percent of kids were living with both parents.

Since then, the decline appears to have stopped.

An additional question regarding millennials' futures is how well they can integrate education, careers, and motherhood. The latest data on Generation X women, born in the early 1970s, suggest this is more possible than it used to be.

American families have gotten smaller over the last 40 years. In 1976, 40 percent of women in their early forties had had four children or more. That fell to 13 percent by 1994, according to a Pew Research Center analysis.

At the same time, however, some well-educated women are having more kids. The proportion of mothers with postgraduate degrees bearing three or more children was 27 percent in 2014, up from 22 percent in 1994.

And women are less likely to get to their mid-40s with no children at all. The decline of childlessness is most striking among those with graduate degrees.