Yanira said she left El Salvador with her three children — ages 8, 11 and 12 — after a local gang tried to recruit her middle child and threatened violence unless he agreed.

When she stepped onto Mexican soil again after being led back across the border by American officials, she broke down.

“I cried and cried,” she recalled.

Mexican officials have said they cannot provide shelter and care for the returnees, essentially leaving them to a network of community groups in Tijuana and elsewhere in the state of Baja California.

But the shelter network has been under extraordinary pressure from the almost-continual arrival of migrants traveling in caravans, who have pushed the centers beyond capacity.

Sister Salomé Limas, a social worker at the Instituto Madre Asunta migrant shelter in Tijuana, said it is currently housing about 120 women and children — in a space designed for 44.

Among the migrants are several families who are seeking asylum in the United States and were returned in recent weeks under the Trump policy.

Sister Salomé said the shelter can house the families until their first court date in the United States, in late March. After that, she is not sure.

“What’s going to happen to them?” she said. “We don’t know.”