The Biden administration has said it will open additional facilities for migrants after images from a detention centre in Texas showed children huddled together in crowded makeshift rooms.
The Texas site, a government-run tent city in Donna at the US-Mexico border, is reportedly housing 1,000 people.
The photos are the first to show conditions at such facilities since President Joe Biden took office.
Critics have blamed Mr Biden for a surge in illegal migration to the US.
Since taking office in January, Mr Biden has removed some of the restrictions for those entering the US introduced by his predecessor, Donald Trump.
His administration has reversed a policy of turning away unaccompanied children at the border, instead opting to process them and place them with sponsoring families in the US.
On Monday, White House Press Secretary Jen Psaki said the US government was working to provide further accommodation for arrivals “in the coming days and weeks”.
“Places where kids can have access to healthcare, can have access to educational resources – even legal resources,” she said.
Her comments came after images released on Monday by Texas Congressman Henry Cuellar, a Democrat, showed children at the facility in Donna sleeping on thin mattresses on the floor under foil blankets.