LONG BEACH, Calif. — A federal emergency shelter in California is starting to receive immigrant children from border facilities in what advocates hope will be an improvement in their care.

About 150 children were expected Thursday at the Long Beach Convention Center at the latest in a series of sites set up across the country following a rise in the number of immigrant children stopped alone on the Mexico border, the Department of Health and Human Services said.

After border facilities grew crowded, the agency opened large-scale temporary shelters to house minors until they can be released to relatives who can care for them in the U.S.

The center in Long Beach is expected to be able to hold up to 1,000 children. Books and stuffed animals were set out on cots. The facility also has nets for indoor soccer and butterfly decorations on the walls, advocates and officials said after a tour.

Children will receive three or four hours of daily classroom time and get to play outdoors. They are expected to be released to family on average in a week to 10 days, Mayor Robert Garcia said. He added that he was told by federal officials that the site could prove to be a model for how to make the shelters as welcoming as possible.

"It looks like a place where children can be," Angelica Salas, executive director of the Coalition for Humane Immigrant Rights, told reporters after the tour.

With more than 20,000 immigrant children currently in government custody, U.S. officials have been scrambling to open such facilities.

The government failed to prepare for an increase in unaccompanied children as President Joe Biden ended some of his predecessor's hardline immigration policies. The Biden administration decided against quickly expelling minors from the country as the Trump administration had done for eight months.

Children are initially taken to border facilities that aren't equipped to house them for longer periods of time. From there, they are being sent to large-scale shelters while case workers assess which relatives are suitable to take them.

The minors will then go through immigration court proceedings to see whether they are eligible to stay in the U.S. or must return to their home countries.