The Department of Homeland Security says it is conducting new medical screenings of all the children in the care of the U.S. Border Patrol.
DHS officials told reporters Wednesday that the screenings are almost complete.
They were ordered after an 8-year-old child died in the custody of U.S. Customs and Border Protection.
The boy, identified by Guatemalan officials as Felipe Gomez Alonzo, was the second migrant child to die in CBP's custody this month.
The department says some children detained in more remote areas were re-screened by emergency medical technicians or Border Patrol agents.
In other places, some children were taken to medical facilities.
DHS wouldn't say exactly how many children are in its custody.