Some youngsters retreat entirely, their eyes empty, bodies limp, their isolation a wall of defiance. Others cannot sit still: watchful, hyperactive, ever uncertain.

Some compulsively jump into the laps of strangers, or grab their legs and hold on for life. And some children, somehow, move past a sudden separation from their parents, tapping a well of resilience.

The Trump administration’s policy of separating migrant children from their parents has alarmed child psychologists and experts who study human development.

It is not clear how long the administration plans to hold onto the 2,000 children in detention centers near the border, nor how long before they are returned to their families.