Two youth care workers at Arizona shelters for migrant children have been charged with sexually assaulting immigrant teenagers, according to court records. They are the latest claims of abuse at government-contracted shelters that have a key role in the Trump administration’s hard-line immigration crackdown.

On Tuesday, the police in Phoenix arrested Fernando Magaz Negrete, 32, on charges of sexual abuse and child molestation after he was seen kissing and fondling a 14-year-old girl in June, the authorities said. That arrest came a day after federal prosecutors detailed their case against another youth worker, Levian D. Pacheco, 25, who is H.I.V. positive and is accused of groping six teenage boys and performing oral sex on two others at a detention center from late August 2016 through July 2017.

While the men worked at separate facilities, both centers are operated by Southwest Key Programs, a Texas nonprofit that has received at least $955 million in federal contracts since 2015 to provide shelters and other services to immigrant children in federal custody. The contractor is one of the largest operators in the highly secretive, billion-dollar business of housing, transporting and watching over migrant children in federal custody on the southern border.

President Trump’s policies on immigration, including the administration’s now-defunct family separation policy, have provided a financial boon to contractors like Southwest Key Programs. The contractors have also come under increased scrutiny for their treatment of immigrants, prompting a top government official on Tuesday to defend the detention centers for families as “more like a summer camp.”