Cal. Veh. Code § 23124

(a) This section applies to a person under the age of 18 years.
(b) Notwithstanding Sections 23123 and 23123.5, a person described in subdivision (a) shall not drive a motor vehicle while using a wireless telephone or an electronic wireless communications device, even if equipped with a hands-free device.
(c) A violation of this section is an infraction punishable by a base fine of twenty dollars ($20) for a first offense and fifty dollars ($50) for each subsequent offense.
(d) A law enforcement officer shall not stop a vehicle for the sole purpose of determining whether the driver is violating subdivision (b).
(e) Subdivision (d) does not prohibit a law enforcement officer from stopping a vehicle for a violation of Section 23123 or 23123.5.
(f) This section does not apply to a person using a wireless telephone or a mobile service device for emergency purposes, including, but not limited to, an emergency call to a law enforcement agency, health care provider, fire department, or other emergency services agency or entity.
(g) For the purposes of this section, “electronic wireless communications device” includes, but is not limited to, a broadband personal communication device, specialized mobile radio device, handheld device or laptop computer with mobile data access, pager, and two-way messaging device.