President Biden has continued a policy started by President Trump of “expelling” back to Mexico many asylum-seeking families crossing the border. Because Biden has also continued to allow unaccompanied children traveling without their parents to stay, many parents and children make the awful decision to separate either after being expelled or preemptively before they can be. This phenomenon—which I’ve documented here and here—is now well known and recognized by everyone, even the Border Patrol. The question is: how big of a driver of the record increases in unaccompanied children is this?

An interesting statistic emerges from the February and March arrest numbers: the total number of Central American children—with or without a parent—this year (51,269) was similar to, but actually lower than, February and March 2019 (57,795), the year when the most significant migration under President Trump occurred. In both years, unaccompanied children were accepted. The only major policy difference is that in the spring of 2019, nearly all families were being immediately released into the United States and not expelled to Mexico, while 39 percent of Northern Triangle families were expelled to Mexico in 2021.

The result can be seen in Figure 1. In February-March 2019, 23 percent of Central American children crossed without a parent. In February-March 2021, nearly twice the share—45 percent—crossed without a parent. This meant that even though there were fewer total children in February and March of this year, there were nearly 10,000 more unaccompanied children. If children had crossed with parents in 2021 with the same frequency as in 2019, 11,178 fewer children would have crossed without their parents, roughly cutting the number in half.

The implication is that perhaps as many as 11,000 children separated from their parents to avoid expulsion to Mexico. It’s impossible to know for certain without surveying them all in detail. In Politico piece from a mid-March, Immigrant Defenders Law Center’s Yliana Johansen-Méndez told journalist Jack Herrera that of the children who the group had interviewed since December, “the number of migrant children whose guardians sent them ahead to cross the border while staying behind make up 33 percent of the total children lawyers met with in shelters.”

Johansen-Méndez said that the numbers were increasing rapidly, already up 26 percent to that point in March, and nearly half of all the unaccompanied children arrested in February and March were arrested in the last two weeks of March. Moreover, her numbers wouldn’t account for the minority of affected parents who never made the trip with their teenage children because they heard that they would be expelled. Whether one half or one third, it is clear that this policy is affecting thousands of children.

This should not surprise anyone. It is a natural response to the incentives of U.S. policy. The government has expelled to Mexico more than 22,500 non-Mexican children with their parents to Mexico since last March. It was always absurd to believe that these people would just stay there, and the government obviously should have expected many unaccompanied children to recross alone to avoid homelessness, destitution, and violence in Mexico once that option became more available in the late summer last year before becoming guaranteed in November. Many more will preemptively self-separate to avoid undergoing expulsion. The Washington Post Mary Beth Sheridan reported this week, yet another family on the brink:

Many migrants say they can’t return home, because they fled violence or spent all their money on the journey. Some are traveling to other border points to cross, or instructing their children to walk into the United States alone, knowing the Biden administration isn’t expelling unaccompanied minors. Xeni said she can’t go back to Honduras because her home was damaged by two devastating hurricanes in November. And she’s desperate to give her children a better life. So desperate, she’s considering a drastic step. “The only option I have is to send the kids over the bridge,” she said.

As long as Biden continues to make that the only option available, the high rates of unaccompanied children and family separations will continue.