Whenever the social worker has cause to believe that there was or is within the county, or residing therein, a person described in Section 300, the social worker shall immediately make any investigation he or she deems necessary to determine whether child welfare services should be offered to the family and whether proceedings in the juvenile court should be commenced. If the social worker determines that it is appropriate to offer child welfare services to the family, the social worker shall make a referral to these services pursuant to Chapter 5 (commencing with Section 16500) of Part 4 of Division 9. No inference regarding the credibility of the allegations or the need for child welfare services shall be drawn from the mere existence of a child custody or visitation dispute.
However, this section does not require an investigation by the social worker with respect to a child delivered or referred to any agency pursuant to Section 307.5. The social worker shall interview any child four years of age or older who is a subject of an investigation, and who is in juvenile hall or other custodial facility, or has been removed to a foster home, to ascertain the child's view of the home environment. If proceedings are commenced, the social worker shall include the substance of the interview in any written report submitted at an adjudicatory hearing, or if no report is then received in evidence, the social worker shall include the substance of the interview in the social study required by Section 358. A referral based on allegations of child abuse from the family court pursuant to Section 3027 of the Family Code shall be investigated to the same extent as any other child abuse allegation.
Ca. Welf. and Inst. Code § 328