▶ Watch Video: DHS secretary on unaccompanied minors at border, effort to unite them with guardians Since President Biden took office, Border Patrol agents have encountered more than 2,100 unaccompanied migrant children who are believed to have left their families voluntarily in order to seek asylum in the U.S, according to government data obtained by CBS News. Between January 20 and April 5, Border Patrol agents came across at least 2,121 unaccompanied migrant children who had been previously expelled under the public health law known as Title 42 when they tried to cross with their families. While most single adults and some families arriving at the southwest border are turned away under Title 42 without being able to apply for asylum, the Biden administration made an exception for unaccompanied children, who are being transferred to the Department Health and Human Services (HHS), as required by anti-trafficking law. The Trump administration first started relying on Title 42 during the COVID-19 pandemic to expel migrants. And the continued use of the Title 42 policy has enabled the Biden administration to turn back tens of thousands more migrants, slowing down the fulfillment of Mr. Biden’s campaign promise to to restore U.S. asylum. The Customs and Border Protection (CBP) data, accessed through a Freedom of Information Act request, offers a small window into a phenomenon that advocates suggest has, in part, been fueling record arrivals of unaccompanied children to the southern border. During a call with reporters on Sunday, Homeland Security Secretary Alejandro Mayorkas acknowledged that his department has been tracking these cases. “We have certainly, anecdotally, learned of the fact that some families self-separate so that their children can arrive at the border. That is something that we are looking very carefully at,” Mayorkas when asked by CBS News whether these self-separations are part of the review of the Title 42 rule. Mayorkas expressed sympathy for parents who are sending their children off on the long trek to the border by themselves. “The circumstances of desperation that lead parents to have their children travel alone from the Northern Triangle countries to the southwest border is no different than the desperation that causes parents to do that,” Mayorkas added. A record number of unaccompanied migrant children entered U.S. custody along the southern border in March, with high concentrations of children passing through the Rio Grande Valley. Since February, U.S. officials in south Texas have encountered 715 unaccompanied children who were previously expelled with their families to Mexico under Title 42, Brian Hastings, the Border Patrol chief in the Rio Grande Valley told reporters during a tour of the CBP holding facility in Donna, Texas, Thursday. “There’s self-separation occurring, I can guarantee you that,” Deputy U.S. Border Patrol Chief Raul Ortiz told a pool of reporters during a ride-along with border patrol officials in late March. “We know we’ve seen that on occasion because we’ve apprehended these [unaccompanied migrant] kids previously, as a family unit. So that’s one of those things that we are awfully concerned about.” In November 2020, a federal judge barred the Trump administration from deporting lone migrant children arriving at the U.S.-Mexico without allowing them a chance to seek humanitarian refuge, as mandated by Congress. “They should all be going back, all be going back. The only people we’re not going to let sit there on the other side of the Rio Grande by themselves with no help are children,” President Joe Biden said during a press conference, in late March. Neither President Biden nor his administration have signaled any plan to suspend Title 42 in the immediate future. “Title 42 is still in place,” a senior administration official told reporters during a briefing, Thursday. “As you know, there’s an exception for unaccompanied kids. And we’ve really been focused on making sure we can process those kids in a safe and orderly manner.” “The ultimate vision is to have a fair and orderly immigration system and to be able to process people seeking asylum,” the official added. “But Title 42 is still in place, other than the exceptions.” CBP did not respond to a request for comment from CBS News.