Originally published 2018-07-09.
Border wall between Texas and Mexico. Photo: Westlee Jay Appleton/Shutterstock
Decades of child-development research point the same way: forcibly separating young children from their parents, especially in a frightening setting and without a familiar adult to comfort them, can trigger what scientists call toxic stress. Prolonged toxic stress can affect brain development, emotional health and even physical health later in life. That body of evidence is why paediatricians, psychologists and psychiatrists spoke out so forcefully in 2018, when the United States separated thousands of migrant children from their parents at the Mexican border.
This article explains what the research says, what happened under the 2018 "zero tolerance" policy, and what is known about the children affected.
What happened at the border in 2018
On 6 April 2018, Attorney General Jeff Sessions told federal prosecutors to adopt a "zero tolerance" approach to people crossing the border without authorisation. On 7 May he announced that parents crossing with children would be prosecuted, which meant the children were taken from them and treated as unaccompanied minors.
The children were first held by Border Patrol, usually for up to around three days, and then moved into shelters run under contract to the Department of Health and Human Services (HHS) or placed with sponsors. PBS reported that nearly 2,000 children were separated between 19 April and 31 May 2018 alone, and by June about 2,300 were in HHS custody.
Separations had actually begun earlier. A pilot programme in El Paso between mid-2017 and late 2017 separated hundreds of family members, and government reviews later found a steep rise in separations that summer, before the policy was announced. Later counts put the total number of children separated under the first Trump administration at around 5,500.
I want to take a moment to address the current illegal immigration crisis on the Southern Border...it has been going on for many, many decades... pic.twitter.com/1F7EK9Ef88
— Donald J. Trump (@realDonaldTrump) June 19, 2018
As the outcry grew, President Trump posted the message above on 19 June 2018, describing the situation as an "illegal immigration crisis". The next day, 20 June, he signed an executive order ending family separations at the border.
How stress works in a child's body
Harvard's Center for the Developing Child, led by paediatrician Jack Shonkoff, describes three kinds of stress response:
- Positive stress: brief, mild spikes in heart rate and stress hormones, such as a first day at nursery or a vaccination with a parent nearby. This is a normal part of growing up.
- Tolerable stress: stronger, longer reactions to serious events such as a death in the family or a natural disaster. If the stress is time-limited and caring adults help the child cope, the brain and body recover.
- Toxic stress: strong, frequent or prolonged adversity without supportive relationships to buffer it. The body's alarm systems stay switched on, and that constant activation becomes harmful.
When a child feels threatened, the amygdala raises the alarm, the hypothalamus signals the adrenal glands, and adrenaline and cortisol flood the body. Heart rate, breathing and blood pressure rise. Normally, comfort from a trusted adult helps switch the system off. Remove that adult, and the alarm can keep ringing.
Why removing a parent is so harmful
The key point in the research is that the parent is not just one more factor. For a young child, a familiar caregiver is the main thing that keeps stress tolerable. Separation therefore does two things at once: it creates a frightening event and removes the child's main source of protection from it.
Speaking to PBS NewsHour in June 2018, Shonkoff put it bluntly: "Taking children away from their mothers is harmful to them." He pointed to hundreds of studies over several decades and warned that the risks grow the longer a separation lasts.
The Harvard center notes that toxic stress can disrupt the forming of neural connections, particularly in areas linked to language, attention and decision-making. Adversity also tends to accumulate: the more adverse childhood experiences a person has, the higher the risk later of conditions such as heart disease, diabetes, depression and substance use problems. That link comes from research on Adverse Childhood Experiences (ACEs), which tracks how events such as abuse, neglect and household dysfunction relate to adult health.
Researchers are careful to add that outcomes are not fixed. A child's age, how long the separation lasts, the conditions of care and the support available afterwards all matter. Not every separated child will suffer lasting damage, but the risk is real and well documented.
What doctors and psychologists said
Medical organisations were unusually united. The American Academy of Pediatrics, the American College of Physicians and the American Psychiatric Association all urged the administration to stop separating families. Colleen Kraft, then president of the American Academy of Pediatrics, visited a shelter in Texas and told PBS that staff were not allowed to touch or hold the children. She described the policy as inflicting toxic stress on them.
Thousands of mental-health professionals and organisations also signed a petition against the policy. Its most quoted line warned that separated children could grow up with "the shrapnel of this traumatic experience embedded in their minds."
Later government reviews supported those warnings. Inspectors from HHS reported that separated children in shelters showed fear, feelings of abandonment and symptoms of post-traumatic stress.
Court orders and reunification
On 26 June 2018, US District Judge Dana Sabraw in San Diego issued a nationwide injunction in the case Ms. L. v. ICE, brought by the American Civil Liberties Union. He ordered that children under five be reunited with their parents within 14 days and older children within 30 days.
Reunification proved slow and incomplete. Many parents had already been deported, and record-keeping linking children to parents was poor. Years later, lawyers and the ACLU said hundreds and then possibly as many as 2,000 children had still not been reunited or located. In December 2023 the court approved a settlement that limits future separations and provides support for reunification, legal access, housing and medical care.
Lessons for families and caregivers
The science behind this story applies far beyond the border. Children face separations from parents because of hospital stays, military deployments, imprisonment, divorce or foster care. Research on toxic stress suggests several practical lessons:
- Keep a familiar adult involved. A trusted caregiver, even part-time, is the strongest buffer against harmful stress.
- Keep separations short and predictable. Clear explanations and regular contact help a child feel safer.
- Allow touch and comfort. Holding and reassuring a frightened child helps calm the stress response.
- Look for signs of distress. Sleep problems, regression, withdrawal or new fears can signal that a child needs extra support. If worries persist, talk to a doctor or a child psychologist.
Supportive relationships, provided as early as possible, can prevent or even reverse much of the damage toxic stress causes. That is the hopeful side of the research, and the reason experts insisted in 2018 that the fastest possible reunification mattered so much.
Sources: Harvard Center on the Developing Child: Toxic Stress; PBS NewsHour: How the toxic stress of family separation can harm a child (18 June 2018); Wikipedia: Trump administration family separation policy; Texas Tribune: Federal judge blocks separation of migrant children (26 June 2018); original reporting by IFLScience.
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