In California, any minor, whether union or non-union, performer or background talent, working in the entertainment industry, must hold a valid and current Entertainment Work Permit.
Here are the procedures for obatining a permit.
You can create an account and apply online for the permit.
A permit is valid for 6 months and can be renewed online. However, the permit will be deemed invalid if parents or legal guardians have not established a 'Coogan Account' within 7 business days after a minor’s employment contract is signed, and provided the minor’s employer with a copy of a trustee’s statement (evidencing proof of the account) within 10 business days after the start of employment (see The Coogan Law page on this site.) This does not apply to minor background ('extras') talent.
NEW LAW - applicants for entertainment work permits between the ages of 14 and 17, must also complete sexual harassment prevention training before obtaining the work permit.
Online training in sexual harassment prevention, retaliation, and reporting resources can be obtained at TalentElevate.com
California Child Labor Law requires that productions, including film-school student films, provide a California Studio Teacher/Welfare Worker when engaging minors for entertainment or promotional purposes.
This also refers to minors who are employed as background talent (aka: 'extras') for any production.