Cal. Ed. Code § 48002
The parent or guardian of a child shall, prior to the admission of the child to the kindergarten or first grade of a school district, present proof to the authorities of the district evidencing that the child is of the minimum age fixed by law for admission thereto. The method of proof of age shall be prescribed by the governing board, and the evidence may be in the form of a certified copy of a birth record or a statement by the local registrar or a county recorder certifying the date of birth, or a baptism certificate duly attested, or a passport, or, when none of the foregoing is obtainable, an affidavit of the parent, guardian, or custodian of the minor, or any other appropriate means of proving the age of the child as prescribed by the governing board of the school district.
Ca. Educ. Code § 48002