Justice Department lawyer Sarah Fabian said officials have now identified 102 children in that age group and would return at least 54 of them to their parents by Tuesday.
The humanitarian crisis caused by Donald Trump's "zero tolerance" immigration policy has resulted in thousands of young children being separated from their parents at the border and relocated to hastily constructed and poorly managed prison camps around the country.
On June 20, the Department of Health and Human Services said there were 2,053 children from separated families in its care.
In a June 26 ruling, US District Judge Dana M. Sabraw in San Diego ordered federal officials to reunite families within 30 days. "You have taken the child from the parent". As for the rest, she claimed, three were brought by someone who is not their biological parent, three have parents with serious criminal records that bar reunification, five have parents with something on their record that requires further investigation, 12 have parents either in local or federal criminal detention who must serve time before being transferred to ICE, 18 have parents who were lost by the administration after their deportation or release into the US, and four have been approved for release to a non-parent sponsor.
Sabraw also blocked the administration from deporting adults without their children unless the parent "affirmatively, knowingly, and voluntarily declines to be reunited with the child" prior to being expelled from the country.
The administration says federal law requires it to ensure that children are safe - and that, it contended, calls for more time.
Trump reversed course on June 20 amid an worldwide outcry and said families should remain together. According to HHS, it's because the number of immigrant children in the agency's care is always in flux - and because they are working with other agencies to cross-check the numbers they have.More news: Najib Razak: Former Malaysian leader charged with criminal breach of trust
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The motion includes hundreds of pages of sworn declarations from migrant parents and their advocates detailing alleged experiences that mothers, fathers and children have endured while trying to seek asylum in the United States.
"DNA testing is intrusive and makes parents nervous", he said.
Sabraw instead directed the government to provide more information over the weekend and set a Monday morning hearing to reconsider the deadlines.
"To our knowledge, this is a cheek swab and is being done to expedite parental verification and ensuring reunification with verified parents due to child welfare concerns", one official told CNN.
"I believe that they can still reunite some [more] individuals by tomorrow", Gelernt said Monday, according to the Post. "It's outrageous. The government has a choice here and that choice is to release people on bond and then reunification could happen immediately".
ICE has so far flown 23 parents on commercial airlines to detention facilities closer to where their children are being housed to facilitate reunions.
While the judge did not revise the Tuesday deadline, it remains unlikely that all "tender age" children will be reunited with their parents by that original date.