The female sect members wear distinctive long gowns
A Texas judge has ordered that 416 children, removed from a polygamous sect by police, remain in state custody for genetic testing.
Welfare officers had told the judge they had been unable to determine which parents the children were related to.
The ruling comes after officials said some of the girls may have had babies when they were just 13 years old.
The closed community was first raided amid reports that a 16-year-old girl was physically and sexually abused.
Detectives are looking for evidence of a marriage between the girl and a 50-year-old man.
She is reported to have been beaten and raped by her older husband and to be pregnant again eight months after giving birth to her first child when she was 15.
The legal age of sexual consent in Texas is 17.
The girl has not yet been identified, but all children living on the isolated Yearning for Zion ranch aged between six months and 17 years of age were placed in emergency state custody.
The adults in the Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS) group, which broke away from the mainstream Mormon Church more than a century ago when polygamy was banned, say they are being persecuted for their religious beliefs.
The sect has built a large church at the Yearning For Zion ranch
Members believe a man must marry at least three wives in order to ascend to heaven. Women are taught that their path to heaven depends on being subservient to their husband.
Group members live in large extended families, and the sect has been accused of forcing young girls into polygamous marriages, a claim it denies.
Child protection officials said group members were evasive when questioned, making it hard to determine exact parenthood, and that DNA testing was necessary.
Child Protective Services supervisor Angie Voss, testifying in Friday's custody hearing, told the court there was a "culture of young girls being pregnant by older men" at the YFZ ranch.
Ms Voss said the girls were in danger of sexual abuse and the boys were being "groomed" to become perpetrators, AFP news agency reports.
An expert on children in cults told the court that the girls may have believed that marrying much older men was their free choice because they had been raised in that belief.
Church members arriving at the Texas court
"Obedience is a very important part of their belief system," said Bruce Perry.
Although many of the adults and children at the YFZ ranch seemed emotionally healthy, the sect's belief system was "abusive", he added.
"The culture is very authoritarian."
Polygamy is illegal in the US, but the authorities have reportedly been reluctant to confront the FLDS for fear of sparking a tragedy similar to the 1993 siege of the Branch Davidian sect in Waco, Texas, which led to the deaths of about 80 members.
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