Donald Trump on Wednesday (June 20) issued an executive order rescinding the policy of separating the children of immigrants and refugees from their parents at the US-Mexico border. But 2,342 children have already been forcibly separated from their parents—exposing them to the kind of stress experts say can have serious, negative long-term consequences for their development. And the order signed by Trump makes no move to reunite those children with their families.

Adversity in general is bad for kids. Things like poverty, racism, abuse, exposure to violence abuse can all produce what neuroscientists and development experts call toxic stress. Those issues do not have simple solutions. But the forcible, sudden separation of children from their parents is entirely avoidable.

“Here we have taken away what science has said is the most potent protector of children in the face of any adversity—the stability of the parent-child relationship,” says Jack Shonkoff, director of the Center on the Developing Child at Harvard University.

“This is not a scientific issue—it’s a fundamental, moral disaster.”

Why family separations are so devastating

When children are forcibly, abruptly separated from a parent or trusted caregiver, stress hormones like adrenaline and cortisol flood their systems. Over time, those hormones can start killing off neurons, causing both short- and long-term consequences that may cause learning and behavioral problems and/or physical and mental health issues, Shonkoff explains.

Children’s stress response systems, if persistently triggered over more than a brief encounter, can affect the immune system, the cardiovascular system, the metabolic system—and even alter the physical structure of the brain. The longer the separation, the worse the impact of the stress is likely to be.

“Every day that goes by that they remain separated from their parents is producing continuing activation of their stress responses, which is having a wear and tear effect on their developing brain and all of their biological systems,” Shonkoff says.

According to the attachment theory, developed in 1958 by John Bowlby and Mary Ainsworth, young children’s sense of security is rooted in their relationships with caregivers. That in turn shapes their social, cognitive, and emotional regulation skills. Separating a child from the caregiver puts the child’s long-term development at risk.

“The effect is catastrophic,” Charles Nelson, a pediatrics professor at Harvard Medical School, told the Washington Post. “There’s so much research on this that if people paid attention at all to the science, they would never do this.”

Since 2000, Nelson and his team have studied thousands of Romanian orphans to understand the neurological impact of separating children from their parents. They found that children separated from their parents in the first two years of life scored lower on IQ tests later in life. Their self-regulation was worse, and their stress reaction systems seemed broken: the things that would cause a typically-developing child to stress out would not have the same effect on them. MRI scans showed that by age eight, these children had less gray and white matter in their brains than children raised by their own families. (White matter is the “information super highway” that moves information around, whereas gray matter is the brain’s central processor.) “Nelson’s work revealed that the orphans’ brains bear marks of neglect,” Nature wrote.

“Children who experience profound neglect early in life, if you don’t reverse that by the age of two, the chance they will end up with poor development outcomes is high,” Nelson told Quartz.

The US government’s policy is intended to be a temporary separation, not a permanent removal. But once parents and children have been separated by the US government, reuniting them can be incredibly difficult. As The Guardian reports, “Some parents have struggled to find their children, some of whom are being flown to shelters around the country. With no clear process in place, it’s possible some families will never be reunited.”

Science shows there can be enormous consequence to breaking that bond. ”As a rule, the longer a child spends in an adverse or neglectful environment, the more difficult it will be to shift that child’s developmental trajectory back to even keel,” said Nelson.

“The only buffer you have is a parent. Take that way and everything falls apart.”

Shonkoff is quick to point out that the children being taken from their parents and housed in temporary shelters by the Department of Health and Human Services are already at risk. They have been traveling for weeks or months, usually fleeing from various other forms of adversity—drugs, violence, poverty—and the sole, and most important, source of comfort and stability they have had through that disorienting experience was a parent.

“The unexpected forcible separation from your parents is worse than the ravages of being in a war zone, or being a victim of oppression, or living in deep poverty,” Shonkoff told Quartz. “In all of those, the only buffer you have is a parent. Take that way and everything falls apart.”

What happens to the children in US custody?

The separation is hurtful enough to children’s development; but the conditions of custody themselves can also add to the toxic stress experienced by these kids. And there’s reason to believe that the US government is not always a trustworthy custodian.

For example, a 2016 report found that the Department of Health and Human Services unwittingly released a dozen minors into the custody of human traffickers. And an investigation by The Texas Tribune and Reveal found that one of the shelters funded by the government to house and educate children separated from their parents, the Shiloh Treatment Center, has repeatedly abused and neglected children. A recent court filing with the California District Court alleges that children in the care of Shiloh were forcibly injected with psychotropic medications and told that they would not be released or see their parents unless they took the medication. Immigrant children being housed at a juvenile detention center in Virginia allege that they were handcuffed, beaten, and put into solitary confinement.

Shonkoff has been studying the effect of stress on development since he became a pediatrician in the South Bronx 35 years ago. People have been asking him the same question: What can we do to help? His response is crystal clear: ”There’s just one program that should be a priority—to reunite them with their parents immediately,” he says. “Not minimize the consequences of the separation.”

“If children were being fed poison—it’s like asking the question, ‘What’s the antidote for the poison?’ The first thing is to stop giving them poison.”

What happens next

Under the Trump administration’s “zero-tolerance” policy, 100% of immigrants attempting to make unauthorized entry into the US at the Mexico border are referred for criminal prosecution. That policy still stands. But under the new executive order, immigration officials from the Office of Refugee Resettlement, which handles the placement of undocumented immigrant children into shelters or with sponsors, will find or build facilities that can hold parents and children together. That could take time.

The language of the executive order has been left intentionally vague. It states that it will be the policy of the administration to detain families together “where appropriate and consistent with law and available resources.” The order to keep families together also only applies to children traveling with one or more parent—but many of the kids crossing the border are traveling with another family member, like a grandparent or a sibling.

In other words, the president’s executive order has not closed the loopholes that permitted these types of family separations to happen in the first place. And it does little to address the trauma and potential long-lasting damage that the US government needlessly inflicted on the more than 2,300 children.

Shonkoff and Nelson say that is always possible to help kids who have suffered trauma. Indeed, we must. “It’s never too late,” Shonkoff said. But every moment matters. Reunification needs to happen immediately, and future policies must be grounded in the incontrovertible biology of parent-child bonds.

Read more from our series on Rewiring Childhood. This reporting is part of a series supported by a grant from the Bernard van Leer Foundation. The author’s views are not necessarily those of the Bernard van Leer Foundation.