If approved, the plan would have closed detention facilities that are designed to house families and replaced them with separate shelters for adults and children. The White House supported the move and convened a group of officials from several federal agencies to consider its merits. But the Department of Homeland Security has said the policy was never adopted.

Children removed from their families are taken to shelters run by nongovernmental organizations. There, workers seek to identify a relative or guardian in the United States who can take over the child’s care. But if no such adult is available, the children can languish in custody indefinitely. Operators of these facilities say they are often unable to locate the parents of separated children because the children arrive without proper records.

Once a child has entered the shelter system, there is no firm process to determine whether they have been separated from someone who was legitimately their parent, or for reuniting parents and children who had been mistakenly separated, said a Border Patrol official, who was not authorized to discuss the agency’s policies publicly.

“The idea of punishing parents who are trying to save their children’s lives, and punishing children for being brought to safety by their parents by separating them, is fundamentally cruel and un-American,” said Michelle Brané, director of the Migrant Rights and Justice program at the Women’s Refugee Commission, an advocacy group that conducts interviews and monitoring at immigration detention centers, including those that house children. “It really to me is just a horrific ‘Sophie’s Choice’ for a mom.”

Mirian has pinballed across Texas, held at various times in three other detention centers. She is part of a lawsuit filed by the American Civil Liberties Union on behalf of many immigrant parents seeking to prohibit family separations at the border.

Her son’s name, along with Mirian’s surname, are being withheld for their safety. But in a declaration she filed in that case, she said she was never told why her son was being taken away from her. Since February, the only word she has received about him has come from a case manager at the facility in San Antonio where he is being held. Her son asked about her and “cried all the time” in the days after he arrived at the facility, the case worker said, adding that the boy had developed an ear infection and a cough.