WASHINGTON, June 13 -- The Trump administration has found a new target for its deportation machinery: children. In a widening investigation laid out this week, federal officials are directing Immigration and Customs Enforcement to track down hundreds of thousands of unaccompanied minors who crossed the southern border without a parent, while prosecuting the very adults who later took them in. The government calls this protecting children from traffickers. What it looks like, in practice, is the state hunting the most vulnerable people in the immigration system and punishing the families who tried to shelter them.

The Washington Post reported that the administration is broadening its probe into the record number of children who arrived al...