LOS ANGELES (CBS) — Call it a phenomenon of unmarried… with children.

The number of unmarried American couples – living with children – has jumped twelve-fold since 1970, according to a recent report released by the National Marriage Project at the University of Virginia.

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“Most couples are almost twice as likely to break up compared to kids born to married couples, so the increase in cohabitation is leading to more family instability in America,” said Brad Wilcox, director of the Project.

Researchers claim families headed by cohabitating parents are not as stable and safe.

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“Abuse statistics rely upon the 2010 federal report Congress releases every four years that looks at trends in child abuse and particular report broke down child abuse trends by family structure. The most risky place for a child in America was a household where the child was living with her mother and her mother’s boyfriend,” Wilcox said.

Kids are more likely, now to live with parents who are not married, than ones who have divorced, the report found.

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Researchers say cohabitating parents tend to have less money and education than their married counter-parts.