Yeni González left her home in rural Guatemala in mid-May. Days later, she crossed the United States border, by night, with her three young children. They were picked up by Border Patrol, she said, and taken to a detention center near Yuma, Ariz.

At 5 one morning, agents woke the children there and took them away.

Ms. González’s children — Deyuin, Jamelin and Lester — are among more than 2,000 young migrants who were separated from their adult relatives under the Trump Administration’s “zero-tolerance” policy.

Despite President Trump’s executive order ending separations and a judge’s order calling on federal authorities to put families back together in no more than 30 days, most families have not been reunited.

This week, Ms. González’s family became the rare exception.

“New York,” she said in Spanish when she spotted the skyline from a car. “My whole heart is there.”