W. BRADFORD WILCOX is Director of the National Marriage Project at the University of Virginia and a visiting scholar at the American Enterprise Institute. LAURIE DeROSE is research director of the World Family Map Project and a professor of sociology at Georgetown University.
From the United States to the United Kingdom, from Peru to the Philippines, marriage is in retreat  and cohabitation  is on the advance. The implications of this shift for adults are much debated; some see it as an important indicator of liberation , others see it as a troubling sign of growing social isolation . But even more important might be the impact on kids.
In the United States, the picture is somewhat dark. Today, a growing share of children are born to cohabiting couples (about 20 percent now), and such children are approximately twice  as likely to see their parents break up by the time they turn 12, compared to children born to married parents. What’s more, even among highly educated American couples with children, cohabitation is about twice as unstable as marriage: 49 percent of college-educated mothers will break up  with their partner before their child turns 12 if they were cohabiting at the time of that child’s birth, compared to just 18 percent of mothers who were married at that point. In the United States, then, marriage comes with a substantial stability premium for children.
This matters because children are more likely to thrive  on stable routines with stable caregivers. Family instability is, by contrast, risky. As sociologist Andrew Cherlin, one of the world’s preeminent family sociologists, observed, “Some children seem to have difficulty adjusting to a series of parents and parents’ partners moving in and out of their home.” Children who experience their parents’ breakup and then additional family transitions are, among other things, more likely  to be unhappy and to be disruptive in school as well as to end up pregnant as a teenager and without a college degree . It is precisely the endemic instability associated with cohabitation in the United States that has led family scholars to express concern. Richard Reeves, co-director of the Center on Children and Families  at the Brookings Institution, has no moral qualms about cohabitation, but he is concerned  by its relative instability in the