“This girl would stop crying if her mother was there, but we couldn’t bring her mother to her,” Kraft said. “We could feel the trauma that was going on there.”

This trauma, she explained, can permanently affect these children’s brains, especially if it occurs early in childhood. Separation from a parent induces stress hormones, which course quickly through kids’ small bodies. Parents can normally help children work through their stress—but not if they aren’t there.

Studies show that high levels of cortisol, one of these stress hormones, can suppress the immune system and change the architecture of a developing brain, according to the National Scientific Council on the Developing Child. Another stress chemical, corticotropin-releasing hormone, can damage the hippocampus, which plays a major role in learning and memory.

The brain develops rapidly before the age of 3, with some connections strengthening and some being pruned away. In healthy, normal kids, synaptic connections related to learning, playing, and social skills are being formed during the toddler years. But, as Kraft explained, in children who have unrelenting stress, the strongest connections in the brain are those related to fear, aggression, and anxiety.

“If you have a whole bunch of bad experiences growing up, you set up your brain in such a way that it’s your expectation that that’s what life is about,” James Perrin, a past president of the American Academy of Pediatrics, told me in 2014.

As the kids grow, the brain starts pruning some of the weaker synaptic connections while keeping the stronger ones. Healthy kids’ brains will keep the connections related to learning or resilience, while perhaps wiping away the small hiccups of childhood. But in kids who have suffered toxic stress, the enduring connections will be the ones related to fear and anxiety, Kraft explained, while those related to learning or relating socially might fade.

Many kids like this, she said, “don’t develop speech, they don’t develop the social and emotional bonds, don’t develop gross motor function [normally]. It leads to very significant developmental delay.”

In other words, keeping kids away from their families does not just emotionally wound them. It biologically wounds them as well—in some cases forever.