(CNN) One is a former hospital. Another is a retrofitted superstore. One is a tent city with the capacity to grow.

These are the places where most infants and children are held after they're separated from their families, who crossed the US-Mexico border without prior authorization.

Children are sent to different facilities across the country depending on their age, gender, history of behavioral issues or criminal activity, or medical needs. These centers are overseen by the Department of Health and Human Services' Office of Refugee Resettlement, which said the average stay is 56 days.

Some are newly built " tender age " facilities to accommodate the influx of children under 13 who have been separated from their parents under the Trump administration's zero-tolerance immigration enforcement policy. One of those facilities is a former private home about 20 miles from the US-Mexico border in Texas town of Combes, operated by Southwest Key Programs.

A set of black strollers and a small playground were the only visible signs of the roughly 60 children -- ranging in age from infants to 10 years old -- housed inside.

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