Many of the young immigrants, a group broadly known as Dreamers, have vowed to stay. But the choice may not be theirs one day. And in Mexico, those who have already returned from the United States warn: Reintegration is rarely easy.

To be sure, voluntary returnees and deportees say that landing in Mexico can have upsides. They can walk the streets without fear of deportation. They can reconnect with long-lost relatives. They can afford college.

But the positive turns can be overwhelmed by the challenges.

Many arrive in a place they never knew as adults, or do not remember. Some may find themselves alone, their friends and relatives still living in the United States. Some may even wrestle with speaking Spanish.

They may struggle to continue their education, find jobs and make their experience in the United States count for something in Mexico.

Their return can carry a stigma: the shame of a deported criminal, or a sign of utter failure.

“The early days was just, like, culture shock, man,” said Mr. Aguilar, who had grown up in what he called “a small white Mormon town” in Utah.

After returning to Mexico, “I isolated myself in my room pretty much,” he said. “Isolation and depression, trying to figure out what was going on, how I ended up living in Mexico.”