The head of U.S. Health and Human Services says reports of unaccompanied migrant children being forced to stay overnight in parked buses at the Dallas convention center are “completely unacceptable” if true. Secretary Xavier Becerra said Friday that the agency is investigating. It’s unclear how many children were kept on buses overnight at the Kay Bailey Hutchison Convention Center. Dr. Amy Cohen, a psychiatrist and child advocate, says a 15-year-old Honduran boy she’s working with was held from Saturday to Wednesday and that boy encountered at least three other children who were held as long. Transportation contractor MVM Inc. says one child was held beyond four hours.