The Justice Department told the Associated Press it's "worked tirelessly" since Friday to try to reunite migrant children with their families.
But the American Civil Liberties Union says it appears the federal government won't hit the court-ordered July 10 deadline.
That's the date a federal judge said all children under the age of 5 had to be reunited with their families.
Over the weekend, the ACLU confirmed to CNN it received a list of almost 100 kids under 5 who'd been separated from their families at the U.S.-Mexico border. On Sunday, it said it didn't believe that "even half" would be reunited with their parents by the deadline.
The Trump administration has already asked for more time. On Friday, the judge refused to issue a blanket extension, but he's scheduled to consider possible exceptions on a case-by-case basis Monday.
Last week, Health and Human Services Secretary Alex Azar estimated fewer than 3,000 migrant kids were in government custody.
All children must be reunited with their families by July 26.
Additional reporting from Newsy affiliate CNN.