They’d had a plan: Elsa Johana Ortiz Enriquez packed up what little she had in Guatemala and traveled across Mexico with her 8-year-old son, Anthony. In a group, they rafted across the Rio Grande into Texas. From there they intended to join her boyfriend, Edgar, who had found a construction job in the United States.

Except it all went wrong. The Border Patrol was waiting as they made their way from the border on May 26, and soon mother and son were in a teeming detention center in southern Texas. The next part unfolded so swiftly that, even now, Ms. Ortiz cannot grasp it: Anthony was sent to a shelter for migrant children. And she was put on a plane back to Guatemala.

“I am completely devastated,” Ms. Ortiz, 25, said in one of a series of video interviews last week from her family home in Guatemala. Her eyes swollen from weeping and her voice subdued, she said she had no idea when or how she would see her son again.

As the federal government continues to separate families as part of a stepped-up enforcement program against those who cross the border illegally, the authorities say that parents are not supposed to be deported without their children. But immigration lawyers say that has happened in several cases. And the separations can be traumatic for parents who now have no clear path to recovering their children.