Upon the filing of a petition under Section 7841, the clerk of the court shall, in accordance with the direction of the court, immediately notify the juvenile probation officer, qualified court investigator, licensed clinical social worker, licensed marriage and family therapist, or the county department designated by the board of supervisors to administer the public social services program, who shall immediately investigate the circumstances of the child and the circumstances which are alleged to bring the child within any of the provisions of Chapter 2 (commencing with Section 7820).