There is perhaps no force more powerful than a group of parents intent on seeing their children again.

Twenty-nine mothers and fathers from Central America, who were deported in 2018 without their under-age children as part of the Trump administration’s so-called zero tolerance policy, arrived on Saturday at the U.S. port of entry between Mexicali, Mexico and Calexico, California. The parents asked border officials to allow them to reenter the U.S. in order to await asylum hearings alongside their children, and after 12 hours of tense deliberation, they were allowed to cross the border.

“He’s waiting for me,” said Jesus, 31, of Honduras, whose 6-year-old son has been in the U.S. foster care system for nearly ten months without his family. Jesus was deported last summer without his kindergarten-age child and has not seen him since. “I hope this time it will be different,” he said.

Because immigrants who have been deported cannot generally reapply for asylum inside the U.S., the parents’ petition at the border was considered a last-ditch effort—the only way that they might be reunited with their children during the months and sometimes years-long wait for a decision on an asylum case. The 29 parents will now either wait out the duration of their asylum proceedings in federal detention or be released to live with sponsors.

The effort, which was coordinated by Al Otro Lado, a Los Angeles based legal services organization, and funded by organizations including Families Belong Together and Together Rising, was designed in part as a direct challenge to the Trump’s immigration policy.

“There were times when I thought, how are we going to pull this off?” Erika Pinheiro, the Litigation & Policy Director at Al Otro Lado, told TIME. “But it’s not over yet. It will be over when they’re reunited with their kids.”

The 29 parents traveled by plane and bus for more than three weeks through Central America to Mexico. They arrived by bus on Saturday morning at the U.S. border near Mexicali, Mexico, where they legally requested admission from U.S. Customs and Border Patrol agents at the international port of entry. All of the parents were admitted to the U.S. for processing by Saturday night.

Under the Trump administration’s zero-tolerance policy, at least 2,700 children were separated from their parents at the border in 2018. A January 2019 Office of Inspector General report suggests that the number may be much higher. Roughly 430 parents were deported from the U.S. last year without their under-age children, who were left in detention, foster care, or with family members. At least 200 migrant children remain separated from their parents today.

Migrant advocates in California on Saturday cheered as the parents walked through the barbed wire-capped gates at the border. Most carried almost nothing in their arms except gifts for their children, including building blocks and toy cars.

For the families and advocates, it was a moment of brief celebration in the midst of an uncertain future. The migrants’ lawyers said that the parents should expect to spend up to six or eight months in detention while their asylum cases are processed.

In the meantime, Jesus held out hope that he would see his little boy soon. He repeatedly scrolled through the same handful photos on his phone that were taken of his son during their time apart. “My son told me he’s in better spirits,” he said, “because I’m on my way.”

Correction, March 4:

The original version of this story contained a misspelling of the legal services organization that organized the parents’ effort. It is Al Otro Lado, not el Otro Lado.

Write to Francesca Trianni at francesca.trianni@time.com.