The horrific accounts of the conditions under which immigrant children are being held has focussed outrage and attention on the Trump Administration’s actions and agenda. But any future reversal of policy will do little to help kids who have already been detained—many of them after being separated from a parent or other relative. The psychological effects of separation and detention have worried experts in child development, and some of them are speaking out. The American Psychological Association, among other groups, has issued multiple statements on the effects of the Trump Administration’s immigration policies, writing that they “pose serious harm to the psychological well-being of immigrant children, their U.S.-born siblings, and other family members.”

I recently spoke with Jack P. Shonkoff—a professor of pediatrics at Harvard Medical School and a professor of child health and development at the Harvard T. H. Chan School of Public Health and Harvard Graduate School of Education—whose research has addressed the consequences of excessive stress on young children. During our conversation, which has been edited for length and clarity, we discussed the psychological effects of detention, the differences in how toddlers and teen-agers register trauma, and why kids who appear to have adapted to their circumstances are often at risk of the most serious problems.

What most concerns you about what we have read about and seen from these border facilities holding children?

Oh, God, where do I begin? I think—to cut through all of the noise, the politics, the back-and-forth on the details—there are just two core issues that are screaming out. One is the fact that the forced and abrupt separation of children from their parents is a huge psychological trauma and assault. The magnitude of the nature of the crisis for a child’s health and well-being cannot be overstated. Abrupt separation from primary caregivers or parents is a major psychological emergency.

The second issue is the prolonged placement of children in institutional settings. Obviously, the two are linked in this particular situation. From the perspective of what we know about children’s health and well-being, what we know about trauma, abrupt separation is one area where we have a lot of research and a lot of evidence about its consequences. But prolonged institutionalization is a separate area in which we have an equally deep research base and knowledge about how damaging that kind of setting is for kids. We are dealing with two very well-studied, serious assaults on the health and well-being of children.

Just to start with separation—and a lot of these kids have been separated from parents or relatives—what sort of case studies are you looking at? What historical examples are you looking at?

It’s a very important question, because in some areas you have classic studies, some iconic investigations that demonstrate this issue. In this case, the importance of the primary relationship—the protective and stable and responsive nature of a parent-child relationship—is not something that comes from a handful of studies. This comes from decades of research across multiple areas. It is a fundamental concept that children, especially when they are young, depend upon stable, responsive relationships for healthy development. When you disrupt those relationships, you pull the rug out from under everything that supports emotional, social, physical well-being. It’s a core scientific principle.

What are the differences between how young kids and older kids respond to separation and what the consequences are?

Obviously, the younger you are the more dependent you are on a stable adult relationship. So, for the toddlers, the preschoolers, the abrupt separation is devastating, not only in terms of what it looks like from the outside but in terms of what is going on inside the body. The healthy development of brain circuits depends upon what we call serve-and-return interaction. It means that healthy brain development requires responsive interaction, not just a passive receipt of stimulation. The child does something, and the adult responds. The adult does something, and the child responds. It’s the essence of what drives healthy brain development. And the brain is biologically wired to expect that kind of responsive interaction, and it uses it to build healthy brain circuits. When that kind of healthy interaction is absent, it triggers a massive stress response inside the body. The heart rate goes up; blood pressure goes up; stress-hormone levels go up; the immune system is activated.

The absence of responsive interaction is, to a young child, potentially life-threatening. Children can’t feed themselves; they can’t take care of themselves; they can’t do anything if they are in pain. So, biologically, you need the interaction from a responsive adult to promote healthy development, and the absence of it triggers this massive stress reaction, which ultimately leads to what we call toxic stress. It disrupts brain circuits, it disrupts the immune system, it disrupts metabolic systems, and it sets the stage for lifelong problems with physical health and mental health.

And for older kids, or teen-agers?

The difference, on the one hand, is that most of these biological systems are now much more mature. The brain has already built its basic circuitry. So now this kind of trauma is managed differently, depending on its history. Kids who have had a reasonably good life—with caring relationships, strong brain architectures, strong immune systems—have more capacity to deal with this kind of a threat. Older kids who have had chronic adversity, who have experienced a lot of stress, are going to be more vulnerable. They have a lower threshold for being seriously disrupted and undermined by this. Older kids have more of a sense of self-agency, of autonomy, so they figure out how to begin to cope with that, as opposed to very young children, whose coping mechanics haven’t yet developed.

For older kids, rather than being completely overwhelmed, you are going to get a variety of responses, ranging from severe anxiety to depression to aggressive behavior to anger. All of them will vary. The youngest children are the most vulnerable to this massive disruption. For older kids, it is more of these behavioral responses.

Many of these kids who crossed the border were already separated from family, and may have seen real violence. You mentioned past history, and I would imagine a lot of them have had histories that would mean more severe consequences.

Yeah, that is absolutely right. From a science point of view, the first organizing principle is that there is tremendous variability. You can’t generalize across the board for children. It will depend a lot on age, a lot on preëxisting trauma, on preëxisting illnesses, and differences in the way kids are wired and in their personalities. Some kids may have a much lower threshold to be seriously withdrawn and depressed, while others are more likely to become aggressive or overtly angry. These are all variations on the same theme, which is the body responding to a massive psychological assault.

To turn to detention, are there specific case studies or research you are drawing from?

Yes, absolutely. And especially for the younger kids. We have research going back more than half a century to look at the impact of institutionalization on child development. Most recently, studies were done on some of the orphanages that were set up in Romania, where young children were given up by their parents early on, because the state banned birth control and poor people had no way they could manage.