BROWNSVILLE, Texas — Life inside the biggest licensed child care facility in the nation for children brought into the U.S. illegally looks more like incarceration than temporary shelter.

The children, a mix of those who crossed into the U.S. unaccompanied and those who were separated from their parents under Attorney General Jeff Sessions’ new zero-tolerance policy, spend 22 hours per day during the week (21 hours on weekends) locked inside a converted former Walmart, packing five into rooms built for four.

It currently houses nearly 1,500 boys ranging from 10 to 17 years old.

NBC News was among the first news organizations granted access to the overcrowded Casa Padre facility.

The average stay at the center in Brownsville is 52 days. After that, minors are placed with a sponsor.

Shelter leaders said they were not notified in advance of the Department of Justice’s recently stated goal to prosecute 100 percent of immigrants crossing into the U.S. illegally. Children are automatically separated from parents referred for criminal prosecution.

The policy has led to a surge in children filling the center above its legal capacity, and has sent officials in Washington scrambling to open temporary tent cities around the country.

Dr. Juan Sanchez, the president of the nonprofit that operates the facility, South West Key, warned that the temporary locations might not have to be licensed or staffed by trained child welfare professionals if they are established on federal land, which the Trump administration has been considering.

The Department of Health and Human Services currently houses about 11,200 immigrant children and is investigating locations including U.S. Air Force bases to house the overflow.

A shelter employee asked a small group of reporters allowed inside the facility to smile at the hundreds of detained migrant kids in line for a meal because “they feel like animals in a cage being looked at.”