Here are a couple of sections from the California Welfare and Institutions Code:
305. Any peace officer may, without a warrant, take into temporary
custody a minor:
(a) When the officer has reasonable cause for believing that the
minor is a person described in Section 300, and, in addition, that
the minor has an immediate need for medical care, or the minor is in
immediate danger of physical or sexual abuse, or the physical
environment or the fact that the child is left unattended poses an
immediate threat to the child's health or safety. In cases in which
the child is left unattended, the peace officer shall first attempt
to contact the child's parent or guardian to determine if the parent
or guardian is able to assume custody of the child. If the parent or
guardian cannot be contacted, the peace officer shall notify a
social worker in the county welfare department to assume custody of
the child.
(b) Who is in a hospital and release of the minor to a parent
poses an immediate danger to the child's health or safety.
(c) Who is a dependent child of the juvenile court, or concerning
whom an order has been made under Section 319, when the officer has
reasonable cause for believing that the minor has violated an order
of the juvenile court or has left any placement ordered by the
juvenile court.
(d) Who is found in any street or public place suffering from any
sickness or injury which requires care, medical treatment,
hospitalization, or other remedial care.
http://www.leginfo.ca.gov/cgi-bin/calawquery?codesection=wic&codebody=Child+neglect&hits=20
Hope that helps.