(CNN)Bryan Chávez carried a bundle of Mother's Day balloons as he headed toward the border.
It had been more than three years since the last time he saw his mom in person -- the day when authorities separated them in 2017. Chávez was 15 at the time, and he feared this moment would never come. Even after he recently learned they'd finally be reunited, he couldn't believe it.
"I was like...am I actually going to see her today or not?" Chavez said. "Because you never know. I was just in the car and I was just thinking, it just sounds unreal."
Chávez and his mom, Sandra Ortíz, were among thousands of migrant families the Trump administration split up as part of widely condemned efforts to deter migration. And this week, they were in the first group of families that the Biden administration said it plans to reunite as part of a new task force's reunification efforts.
A video of their dramatic reunion released by advocacy group Families Belong Together shows the mother and son embracing, sobbing and wiping their eyes at the San Ysidro Port of Entry in San Diego -- the very spot where they'd last crossed the border together in 2017, seeking refuge in the United States.
The pair were among four families reunited this week in a highly publicized effort Department of Homeland Security Secretary Alejandro Mayorkas announced over the weekend.
"The first families reuniting this week are mothers, they are sons, they are daughters, they are children who were 3 years old at the time of separation. They are teenagers who have had to live without their parent during their most formative years," he said.
Immigrant advocates say the US has been dragging its feet
But even as the Biden administration trumpeted the reunions, some advocates who've been working for years to reunite families the government separated have bristled at the suggestion that officials were helping the effort -- accusing the government of dragging its feet rather than facilitating the more than 1,000 reunions that have yet to occur.
"These mothers have been waiting, in danger in Mexico, for over three years," Al Otro Lado said in a statement posted to the organization's Twitter account describing several families the organization represents, adding that the only thing keeping more families from reuniting was a "lack of political will" to do so.
Bryan Chávez and Sandra Ortíz were reunited this week after more than three years apart.
Lee Gelernt, the attorney leading the ACLU's lawsuit over family separations, told CNN that advocates are celebrating with the four families who were able to reunite, but know their work is far from over.
"These are the first four families. It's a long haul. We're negotiating in our class-action lawsuit for all of the families -- we want them all brought back and we want them all to be given legal status. We have to do that if these families have any chance of leading a healthy, productive life ... This is just the beginning," he said.
"It is the tip of it. We have so much work to do. And I think like any major civil rights case, a lot of it is just, are you going to stick with it and grind? And that's what we are hoping and expecting the Biden administration to do. We can't all rest and say, 'it's solved.'"
Gelernt described what it was like to watch another mother reunite with her sons in Philadelphia Tuesday.
"I almost don't have the words to describe it," he said. "It was so emotional, just gut-wrenching, these boys hugging their mother for what seemed like an eternity, all of them sobbing, the extended family sobbing."
According to Al Otro Lado, which is representing Ortíz, the mother and son fled their home in Michoacan, Mexico, after cartels kidnapped and killed Chávez's father and uncle and demanded he join their gang. The mother and son were separated two or three days after arriving in United States in October 2017. Ortíz was deported two weeks later and had to go into hiding, Al Otro Lado said.
"Seeing her in person, being able to give her a hug and everything," Chávez told reporters, felt like a dream -- and like the end of a nightmare.
