As of December, the department had identified 2,737 children who were separated from their parents under the policy and required to be reunified by a federal court order in June 2018.

But that number does not represent the full scope of family separations. Thousands of children may have been separated during an influx that began in 2017, before the accounting required by the court, the report said.

Thus, the total number of children separated from a parent or guardian by immigration authorities is “unknown,” because of the lack of a coordinated formal tracking system between the Office of Refugee Resettlement, the arm of Health and Human Services that takes in the children, and the Department of Homeland Security, which separated them from their parents.