Families hoping to win release for the thousands of migrant children being held by federal immigration authorities are finding they have to navigate an exhausting, intimidating—and sometimes expensive—thicket of requirements before the youngsters can be released. Brenda, a Salvadoran migrant who was separated from her 7-year-old son Kevin at the border on May 27, was charged $576.20 to cover the boy’s airfare from Miami to Virginia. His escort collected the money order at Washington Dulles airport on Friday upon handing over the child to his mother. Under the policy manual of the Office of Refugee Resettlement, sponsors are responsible for paying transportation costs for both the child and any escort, along with fees charged by airlines for handling transport of unaccompanied minors.