"Dark underbelly of cohabitation"

As more children grow up in splintered homes, experts are detecting an unsettling correlation between child abuse and cohabitation.

Brad Wilcox, a sociology professor at the University of Virginia, called abuse "the dark underbelly of cohabitation." He said, "Cohabitation has become quite common, and most people think, 'What's the harm?' The harm is we're increasing a pattern of relationships that's not good for children."

Studies on the link between the two are scarce, but children living in households with unrelated adults are nearly 50 times as likely to die of inflicted injuries. They are at a higher risk for physical and sexual assault if they live in stepfamilies or with single parents. Girls with divorced parents are at a higher risk for sexual assault no matter which parent they live with.

Patrick Fagan, a family-policy specialist with the Family Research Council, said a lack of male role models is partly to blame: "These boyfriends increasingly have been raised without fathers and been abused themselves. … Among the inner-city poor, the turnover of male partners is high. Where's a boy getting the model of what a father is like?"

Fagan authored a 1997 Heritage Foundation paper about child abuse and the disintegration of the American family. Researchers traditionally focused on the correlation between poverty and child abuse, but Fagan argued that researchers should also note "the presence or absence of an adult support." Of course, as marriage becomes a luxury item for the well-off, poor people are becoming less likely to marry.

Robin Wilson, law professor at Washington and Lee University, said an emphasis on family autonomy and privacy can make investigators reluctant to pry: "I hate the fact that something dangerous for children doesn't get responded to because we're afraid of judging someone's lifestyle."