“Parents with children under the age of 5 are being reunited with their children and then released and enrolled into an alternative detention program,” Matthew Albence, Immigration and Customs Enforcement’s executive associate director of enforcement and removal operations, told reporters on Tuesday.

He said that means the migrants will be given ankle bracelets “and released into the community.”

Government officials said they were struggling to meet Tuesday’s court-ordered deadline to reunite 102 migrant children under 5 with their parents; only about one-third were expected to be reunited by then.

The reunions that did happen were chaotic. Parents were warned that pickup and drop-off times could change throughout the day. The federal agency that oversees the care of migrant children, the Department of Health and Human Services, was still conducting background checks on parents into Tuesday morning.

In Phoenix, the reunions were marked by confusion and heartbreak.

As Ms. Lopez and Ms. Pablo waited at a Greyhound station to board eastbound buses, their children called each other sister and brother. They were yet to utter the word “mami,” Spanish for mother, to the women cuddling, stroking and feeding them. But they were calmer, the mothers said.

Darly, who had been potty-trained before the separation, had regressed to diapers. Ederson bounced up and down on his mother’s lap and downed Doritos with gusto. All of the adults were fitted with ankle monitors.

“I want to go with my little sister,” he said, pointing to a 13-month-old named Carmen in the arms of Denis Espinoza, her Honduran father who was released from detention to recover her 20 days after they were separated.