WASHINGTON — The Department of Health and Human Services placed more than a dozen immigrant children in the custody of human traffickers after it failed to conduct background checks of caregivers, according to a Senate report released on Thursday.

Examining how the federal agency processes minors who arrive at the border without a guardian, lawmakers said they found that it had not followed basic practices of child welfare agencies, like making home visits.

The Senate’s Permanent Subcommittee on Investigations opened its inquiry after law enforcement officials uncovered a human trafficking ring in Marion, Ohio, last year. At least six children were lured to the United States from Guatemala with the promise of a better life, then were made to work on egg farms. The children, as young as 14, had been in federal custody before being entrusted to the traffickers.

“It is intolerable that human trafficking — modern-day slavery — could occur in our own backyard,” said Senator Rob Portman, Republican of Ohio and the chairman of the subcommittee. “But what makes the Marion cases even more alarming is that a U.S. government agency was responsible for delivering some of the victims into the hands of their abusers.”