Details are still slowly trickling in about how a migrant shelter in Downtown Long Beach will operate, but on Friday, officials revealed who’s expected to be held there.

Children and their siblings—some as young as 3 years old—will be temporarily housed at the Long Beach Convention Center after being found without their parents along the U.S. border, Mayor Robert Garcia said in a tweet Friday.

“These sibling pairs have been found alone and unaccompanied along the border,” Garcia tweeted. “Our top priority must be family reunification.”

All the children arriving in Long Beach are expected to have sponsors or family members in the U.S. already identified to speed the reunification process.

It’s not yet clear when children will begin arriving.

“Every day it moves closer, but there’s no clear timeline yet,” Garcia told the Press-Telegram.

City officials say the program would run until Aug. 2 at the latest. The Convention Center is expected to hold up to 1,000 children over that time period.

The plan to hold unaccompanied migrant kids at the Convention Center comes as there’s been a significant increase in children arriving without parents at the southern border, many of them fleeing violence, extortion and poverty in Central America.

The U.S. government picked up nearly 19,000 children traveling alone across the Mexican border in March, authorities said Thursday, the largest monthly number ever recorded.

The huge increase in children traveling alone and families has severely strained border holding facilities, which aren’t allowed to hold people for more than three days but often do. It’s left the government scrambling to find space and hire staff to care for children longer term until they can be placed with sponsors.

In late March, the White House contacted Garcia’s office asking for help, and Garcia rallied support for the idea before the City Council approved it this week.

A complex mix of factors in the U.S. and Central America are driving the increase in border crossings. It has coincided with the Biden administration’s decision to exempt unaccompanied children from pandemic-related powers to immediately expel most people from the country without giving them an opportunity to seek asylum. Children are instead released to sponsors in the U.S., usually parents or close relatives, while being allowed to pursue their cases in heavily backlogged immigration courts.

The Border Patrol encountered 18,663 unaccompanied children in March, well above previous highs of 11,475 in May 2019 and 10,620 in June 2014. The agency started publishing the numbers in 2009. Before then, adults made up the vast majority of those crossing the border.

March’s count was roughly double the number of unaccompanied children encountered by the Border Patrol in February and more than five times the number in March 2020.

The Associated Press contributed to this report.

Jeremiah Dobruck is managing editor of the Long Beach Post. Reach him at [email protected] or @jeremiahdobruck on Twitter.