Lisbeth takes out her cellphone and flashes a picture of her foster daughter. Two years ago, the teenager was living on the streets near Miami. Her mother, who was addicted to drugs, would disappear for long stretches at a time, and her father was in jail. The 14-year-old girl would steal noodles and cold cuts from local bodegas to feed herself and her two half-siblings, aged 4 and 5. She wasn’t in school.

Eventually, she was found by staff at the Florida Department of Children and Families, who determined that she was being sold for sex. Her legs were pocked with cigarette burns. “She doesn’t talk about the past,” Lisbeth said.

After child welfare found her, she lived briefly in a group shelter before going to live with Lisbeth and her husband, Rolando (the couple’s last names are being omitted to protect the family’s privacy). Lisbeth and Rolando are courageous people. It’s hard to be a foster parent, harder still to parent a teenager and harder still to parent someone who has suffered the extreme trauma of being trafficked. But the family is part of a small group in Miami involved in Chance, for Citrus Helping Adolescents Negatively Impacted by Commercial Exploitation, one of the first child welfare programs in the country designed specifically for trafficked foster youth.

Miami is one of 13 cities considered by the F.B.I. to be a hub for child sex trafficking. While there are no reliable estimates of how many children have been trafficked in the United States — the most conservative estimates hover around 3,000 — it’s the most vulnerable children who are most often targeted. African-American, Latino, L.G.B.T.Q. and migrant youth are disproportionately victimized, as are children who are homeless or have spent time in foster care. These children are more likely to have histories of trauma, which makes them more susceptible to manipulation by traffickers.