The Alameda County Department of Children and Family Services serves about 300,000 young people. A recent state audit found the department consistently failed to protect children in its care, including 8-year-old Sophia Mason of Hayward. State Sen. Aisha Wahab, who represents California’s District 10, said Alameda County had prior knowledge of Sophia’s situation. “Alameda County knew about the case. Requests for comment from the Social Services Agency and the majority of the Alameda County Board of Supervisors were not immediately returned.