Despite public outrage over the Trump administration’s family separation policy and a court ordering its termination, the administration continues to separate families at the border. Immigration and Customs Enforcement (ICE) deportations also separate families, sending parents into removal proceedings and leaving children behind.

History suggests that family separation, particularly when children are separated from their primary caregivers, most often mothers, will cause enduring harm. The experience of World War II-era Britain shows that even when the conditions of separation were far more favorable than they are today, separating children from their parents was deeply traumatic. Anna Freud even concluded at the time that London children were “less upset by bombing than by evacuation to the country as a protection against it.”

The British government expected German bombs to obliterate London and other major cities as soon as war was declared in 1939. Wanting to ensure the nation’s future, come what may, the government planned “Operation Pied Piper.” Children, pregnant women and mothers of young children were removed from danger zones into “reception areas” in the countryside.

The government provided transportation, and volunteers provided the housing. The conditions weren’t terrible: Unaccompanied children were not “warehoused” or imprisoned. Instead they were placed with families who had volunteered to open their homes in exchange for a small sum. Some took their responsibilities narrowly, providing food, bedding and nothing more, while others took children into their hearts as well as their homes.

The evacuations began on Sept. 1, 1939. By the time war was declared two days later, almost 2 million children had been removed to the countryside, about a third of the qualifying population having volunteered to relocate. “Everyone in my school assembled with our suitcases and gas masks in the playground where we were counted,” recalled one Englishman many years later. “We had no idea where we were going, how long we’d be away or when we’d see our parents again.”

Even though the evacuations were undertaken to protect children, being away from parents — and having no idea what happened to them — was deeply traumatic.

Evacuated children experienced the best outcomes when host families provided consistent loving care, enabling a new attachment to be formed, while fostering frequent contact between children and their parents. A retired banker and his wife in the seaside town of Sidmouth accepted two school-age sisters. After “two days of howling” the girls settled in, Mrs. Green told a “Mass Observation” interviewer, and bonded with their hosts. Monica Lady Salmond took in eight evacuees and exchanged letters with the parents so that the children were able to stay in touch; some children’s mothers came to visit at Salmond’s Eastbourne home, demonstrating that the separation was temporary and purposeful. Salmond formed a tight bond with the children, visiting two girls when they were hospitalized, and later visiting all of them in new host homes after the government decided Eastbourne was no longer safe.

But these were exceptions to a deeply traumatic experience for most children. Expecting rosy-cheeked youngsters thrilled to have a rural holiday, receiving households often received ill, ragged, fearful children instead. Younger children were afraid because they did not know what was going on; older children were afraid because they did.

Rural householders were often aghast at the condition of the urban children who arrived. One volunteer county organizer observed that “the dirt and low standard of living” of those evacuated from Hull and Leeds “had been an eye-opener and an unpleasant shock to the inhabitants of an agricultural county like Lincolnshire.” Hosts were not always generous; some refused to take in children who appeared infected or lice-ridden.

Behavioral problems, such as constant crying, aggressive acting out and mute refusal, were commonly noted after the children came to stay. “Absolute little hooligans” was the general verdict, as evacuees, perhaps traumatized by their sudden removal from home and family, violated household rules. An American eyewitness reported that “they relieved themselves everywhere but the place provided for the purpose” at a house that had taken in half a dozen evacuated children.

By the time the Blitz actually started a year later, most of the children had already returned home. Evacuation efforts thereafter were more improvised, as displaced families and individuals found housing where they could. Eventually, the war damaged or destroyed an estimated two-fifths of the nation’s housing stock, leaving thousands homeless, many of whom were children separated from their families by the war.

It was through studying separated children during the war that the psychologist John Bowlby developed his influential and controversial theory of attachment. Children who endured prolonged separations from their primary caregivers, he observed, experienced the highest levels of trauma. Bowlby concluded that children who formed deep emotional attachments to and trust in the adult figures in their lives were better equipped for survival, but trauma was highly likely for all. In follow-up studies Bowlby observed that affected children showed attachment difficulties later, often exhibiting affectless and even criminal behaviors. The longer the children had been separated from their parents, he deduced, the worse the outcomes.

A psychoanalyst and daughter of Sigmund, Anna Freud arrived at similar conclusions. Along with her companion and colleague Dorothy Burlingame, Freud ran three wartime nurseries in Hampstead. They concluded that wartime hardships were relatively insignificant for children in and of themselves. But these became enormously important when accompanied by the breakup of the family.

The key was whether families stayed together or whether children had been separated from their parents. When families arrived at one of Freud’s “Rest Centers” immediately after a bombing, children showed little disturbance, sleeping, eating and playing normally. But when separated from their mothers, Freud observed, young children exhibited many signs of trauma, such as bed-wetting, aggressive play and uncontrollable and prolonged crying. Others simply became nonresponsive, sitting mute, often refusing to speak, move and, on occasion, eat.

Researchers’ conclusions matched the observations of householders who had hosted evacuated children earlier in the war. While upper-class countryside residents often viewed unwelcome behaviors in children through the lens of class, what they were witnessing, in fact, was childhood trauma. Children who remained with a kind and attentive host family for a prolonged period settled down. Symptoms of trauma, like “howling,” diminished as the children formed new attachments to loving hosts, the kind of women who corresponded and visited with the children they’d hosted for many years after the war ended.

No such opportunities, of course, are being afforded the children now held in U.S. custody or those left behind after their parents’ deportations. The Assistant Inspector-General of the Department of Health and Human Services recently reported that like the British youths during World War II, immigrant children in U.S. custody are traumatized. And staff members at facilities holding children are not prepared to deal with childhood trauma.

Inconsolable crying, despair and even suicidal ideation are not uncommon. Children are haunted by fears about parents with whom they have lost touch, as were child evacuees during the war. Emotional pain is identified physically: One child plaintively said, “Every heartbeat hurt.” Children at U.S. facilities are unable to distinguish between the health-care workers, who might be able to provide some individualized care, and the agents who took their parents away. Front-line staff at these facilities reported to the inspector general’s office that even children who entered the facility with “good coping skills” and were “well-behaved” began to experience real emotional decline after 70 days of internment.

This shouldn’t surprise us.

Temporary wartime evacuees placed in more favorable situations still suffered traumatic effects from being separated from their parents. Although kindness and consistent care, as well as maintaining contact with their parents, diminished children’s trauma in those instances, immigrant children being forcibly separated from their parents have little chance to mitigate the effects of these separations. And while the Trump administration maintains that these policies will serve as a deterrent to future immigration, the only clear effect of these policies is to make children suffer — probably for years to come. Eighty years after British children suffered the effects of wartime separation, and after more than 50 years of research and experience, we cannot use the excuse of ignorance. We know very well what we are doing to these children.