A new holding facility for unaccompanied migrant children previously used as a private dormitory "man camp" for oil field workers could stay open through January 2020, at a cost of $300 million, according to an announcement Monday in the Federal Register.

The site in Carrizo Springs, Texas opened Monday and has a capacity of 1,300 children. Two hundred reside there after day one, a spokesperson for the U.S. Department of Health and Human Services (HHS) told CBS News.

The population at the facility will grow "over a graduated timeframe," according to the notice posted by HHS in the Federal Register, the official journal of the U.S. government. HHS oversees the nation's network of 170 holding facilities — described as shelters by the government.

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The new facility in Carrizo Springs has the third largest capacity in the HHS system, and is one of just two described by the agency as "temporary influx shelters." The other, in Homestead, Florida, is by far the largest facility for unaccompanied migrant children in the country, currently holding about 2,300 kids, with a capacity of 3,200.

A third "temporary" facility will be the only HHS facility operating on a military base: the Fort Sill Army post in Oklahoma. That facility, on the site of a World War II internment camp where Japanese-Americans were forcibly detained, will have a capacity of 1,400.

Though the Carrizo Springs and Homestead facilities are described as "temporary," federal contracts depict plans for potential long-term use of the sites. BCFS, the nonprofit that is running the Carrizo Springs location, is due $50 million for the first 60 days of operation, with as much as $250 million total to be paid if the location remains open through Jan. 31.

The Homestead "temporary" facility has run continuously since April 2018. Federal contract records show Comprehensive Health Services, the company that operates it, is on pace to receive more than half a billion in payments by November. That facility has tripled in size since late 2018.

The "temporary influx shelters" have come under widespread, withering criticism from advocates and politicians. Last week, nearly ever Democratic candidate who participated in presidential debates in Miami, traveled the roughly 30 miles south to the Homestead location. They stood on ladders provided by protesters and peered over the tall green walls that surround the facility, yelling messages of support to the children inside.

Meanwhile, as BCFS and HHS rushed to prepare the Carrizo Springs facility for use, employees of the online retailer Wayfair caught wind of a contract between their company and BCFS. The employees staged a walkout to protest the company's involvement with the facility.

Unaccompanied migrant children in the HHS system are currently held for an average of 45 days while awaiting placement with relatives in the U.S. Some children labeled "unaccompanied" cross the border alone, but many actually arrive with relatives such as aunts, uncles and even older siblings, but are separated by Border Patrol from those adults and placed in facilities for unaccompanied minors. Children are only considered "accompanied" if they cross the border with parents.

In an interview with CBS News inside the Homestead facility Friday, HHS Secretary Alex Azar defended the program and the "temporary influx shelters."

"We're trying to take care of these kids and place them out as quickly as possible to family members," Azar said.

Azar was also asked about allegations by lawyers that children are subject to "prison-like" rules and wrongly told that minor violations — taking too long a shower, hugging a sibling despite a "no touching" policy — could harm their immigration cases.

Azar said after the allegations were made, staff were warned not to do that.

"Well, let me be really clear. That would be completely improper. That would be completely improper. And the staff here have been instructed after that allegation was made that any such behaviors or statements would be wrong and subject to discipline," Azar said.