Five days before the first government-imposed deadline to reunite migrant parents and children who were separated after crossing the Southwest border, immigration authorities are mounting a round-the-clock effort involving hundreds of federal workers to bring the families together, a senior Trump administration official said Thursday.

Nearly 3,000 separated children remained in the government’s care, about 100 of whom were under 5 years of age. The youngest children must be reunited with a parent by Tuesday under a deadline imposed by a federal judge in San Diego.