“With Mexico, the proximity makes it easier to cross more than once,” Lopez said.

The findings come as the federal government has spent weeks racing to deal with an influx of unaccompanied children from Central America and Mexico, six to 10 times what had been the average population before their numbers began multiplying from 2011 to this year.

Before Congress left on Friday for its summer recess, the House approved a change to the 2008 law that requires Central American children be given certain immigration hearings to determine whether they qualify for asylum or other protections.