California Code of Civil Procedure > Code Civ. Proc. §116.410. Standing; Minors and Incompetent Persons
(a) Any person who is at least 18 years of age, or legally emancipated, and mentally competent may be a party to a small claims action.
(b) A minor or incompetent person may appear by a guardian ad litem appointed by a judge of the court in which the action is filed.