The fate of hundreds of undocumented children taken from parents remains unclear a day after President Donald Trump moved to roll back his policy.
He ordered on Wednesday that the children be held with their parents while they are detained on charges of crossing the border illegally.
But under US law, migrant children cannot be detained more than 20 days by immigration officials.
The Pentagon has been asked to prepare up to 20,000 beds for children.
It comes amid US government inquiries into whether they can house unaccompanied children who cross the US-Mexico border on US military bases.
The Department of Health and Human Services (HHS) made the request to the Department of Defense hours after First Lady Melania Trump made a surprise visit to a child migrant detention centre.
Her tour of the federally funded facility in McAllen, Texas, housing dozens of Central American children, came as her husband’s administration sought to quell the firestorm over migrant separations.
