In just one month last year, Tyari Smith Sr. of suburban New Orleans shot and killed his 2-year-old son, Tyari Smith Jr., and his girlfriend, Marie Chavez, because she was considering leaving him and heading back home to California. A week later, 4-month-old Aiden Caro was thrown into a couch by his mother’s boyfriend, Samuel Harris, when Harris could not get him to stop crying. Shortly thereafter, the Louisville baby stopped crying forever. The next week, in Gaston, South Carolina, 5-month-old Joshua Dial was shaken by his mother’s boyfriend “in a manner so violent that the baby immediately lost consciousness and suffered severe brain trauma,” according to local police reports. Joshua died soon thereafter.

Are these tragic cases of fatal child abuse around the nation in one month just random expressions of the dark side of the human condition? Not according to a recent federal study of child abuse and neglect, the Fourth National Incidence Study of Child Abuse and Neglect.

This new federal study indicates that these cases are simply the tip of the abuse iceberg in American life. According to the report, children living with their mother and her boyfriend are about 11 times more likely to be sexually, physically, or emotionally abused than children living with their married biological parents. Likewise, children living with their mother and her boyfriend are six times more likely to be physically, emotionally, or educationally neglected than children living with their married biological parents. In other words, one of the most dangerous places for a child in America to find himself in is a home that includes an unrelated male boyfriend—especially when that boyfriend is left to care for a child by himself.

But children living with their own father and mother do not fare much better if their parents are only cohabiting. The federal study of child abuse found that children living with their cohabiting parents are more than four times more likely to be sexually, physically, or emotionally abused than their peers living in a home headed by their married parents. And they are three times more likely to be physically, emotionally, or educationally neglected than children living with their married biological parents. In other words, a child is not much safer when she is living in a home with her parents if her parents’ relationship does not enjoy the legal, social, and moral status and guidance that marriage confers on relationships.

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This latest study confirms what a mounting body of social science has been telling us for some time now. The science tells us that children are not only more likely to thrive but are also more likely to simply survive when they are raised in an intact home headed by their married parents, rather than in a home headed by a cohabiting couple. For instance, a 2005 study of fatal child abuse in Missouri found that children living with their mother’s boyfriends were more than 45 times more likely to be killed than were children living with their married mother and father.

Cohabitation is also associated with other non-fatal pathologies among children. A 2002 study from the Urban Institute found that 15.7 percent of 6- to 11-year-olds in cohabiting families experienced serious emotional problems (e.g., depression, feelings of inferiority, etc.), compared to just 3.5 percent of children in families headed by married biological or adoptive parents. A 2008 study of more than 12,000 adolescents from across the United States found that teenagers living in a cohabiting household were 116 percent more likely to smoke marijuana, compared to teens living in an intact, married family. And so it goes.

One reason that children do not tend to thrive in cohabiting households, besides the abuse factor, is that these homes are much more unstable than are married households. One recent University of Michigan study found that children born to cohabiting parents were 119 percent more likely to see their parents break up than children born to married parents. And, as anyone who has children can attest, children do not do well when they are exposed to changing routines, homes, and, especially, caretakers.

This growing body of new research has been deliberately ignored by the ACLU, which has been engaged in a longstanding legal campaign to gut state laws designed to support and strengthen marriage as the preferred relationship for the bearing, rearing, and adoption of children. This month in Arkansas, for instance, the ACLU convinced the Arkansas Supreme Court, in Cole v. Arkansas, to strike down a state law that prohibits cohabiting couples from adopting or fostering children. The ACLU argued that the Arkansas law violated federal and state constitutional rights to privacy and served “no child welfare purpose at all.” The Arkansas Supreme Court bought this argument, ruling that the Arkansas law, Act 1, violated cohabitors’ “fundamental right to privacy… to engage in private, consensual, noncommercial intimacy in the privacy of their homes.”

But what about the rights of the children in Arkansas to be raised in a safe and stable home? The state of Arkansas argued, rightly, that cohabiting homes are no place for children in need of safe and stable homes. Infants, toddlers, and older children who have been given up by their parents, or who have been removed by the state from the custody of their parents, need safe and stable homes above all else. And the latest federal study provides yet more evidence that households headed by cohabiting couples are not likely to supply good homes for such children. Apparently, none of this mattered to an Arkansas Supreme Court keen to put adults’ desires ahead of children’s needs.

Thankfully, the family news from the states has not been all bad this month. On Monday, Arizona governor Jan Brewer approved a law that gives married parents preference in the adoption process in her state. Arizona thereby joins a number of other states—such as Mississippi, Utah, and Virginia—that privilege married couples in the adoption process.

Let’s just hope that the courts in Arizona and these other states do not fall prey to the ACLU’s ongoing campaign to disconnect parenthood from marriage. Because—as study after study tells us—children are more likely to thrive and to simply survive when they are raised in an intact, married home. This is no small social fact, given that the primary purpose of family law is not to serve the desires of adults but rather the “best interests” of children.