While everyone should report suspected child abuse, The California Penal Code provides that it is a crime for certain professionals and laypersons who have a special working relationship of contact with children not to report suspected child abuse to the proper authorities. These professionals and laypersons shall report the known or suspected child abuse to a child protective agency immediately or as soon as practically possible by telephone and shall prepare and send a written report thereof within 36 hours of receiving the information concerning the incident.
California Penal Code 11172, subdivision (e) gives mandated reporters who report suspected cases of child abuse absolute immunity, both civilly and criminally, for making such reports. However, any person who fails to report an instance of child abuse as required by the Child Abuse Reporting Act is guilty of a misdemeanor with a punishment not to exceed six months or $1,000 or both.
For Mandated Reporters who suspect child abuse or neglect, your call is required by law (PC 11166)