29 C.F.R. § 570.5
Certificates of age and their effect
(a) To protect an employer from unwitting violation of the minimum age standards under the Act, section 3(1) of the Act provides that “oppressive child labor shall not be deemed to exist by virtue of the employment in any occupation of any person with respect to whom the employer shall have on file an unexpired certificate issued and held pursuant to regulations of the Secretary of Labor certifying that such person is above the oppressive child-labor age.” The provisions of this subpart provide for age certificates based on the best available documentary evidence of age. Certificates issued and effective pursuant to this subpart furnish an employer with proof of the age of a minor employee upon which he may rely in determining whether the minor is at least the minimum age for the occupation in which he is to be employed.
(b) The employment of any minor shall not be deemed to constitute oppressive child labor under the Act if his employer shall have on file an unexpired certificate, issued and held in accordance with this subpart, which shall be either:
(1) A Federal certificate of age, issued by a person authorized by the Administrator of the Wage and Hour Division, showing that such minor is above the oppressive child-labor age applicable to the occupation in which he is employed, or
(2) A State certificate, which may be in the form of and known as an age, employment, or working certificate or permit, issued by or under the supervision of a State agency in a State which has been designated for this purpose by the Administrator showing that such minor is above the oppressive child-labor age applicable to the occupation in which the minor is employed. States so designated are listed in § 570.9(a). Any such certificate shall have the force and effect specified in § 570.9.
(c) The prospective employer of a minor, in order to protect himself from unwitting violation of the Act, should obtain a certificate (as specified in paragraphs (b) (1) and (2) of this section) for the minor if there is any reason to believe that the minor's age may be below the applicable minimum for the occupation in which he is to be employed. Such certificate should always be obtained where the minor claims to be only 1 or 2 years above the applicable minimum age for the occupation in which he is to be employed. It should also be obtained for every minor claiming to be older than 2 years above the applicable minimum age if his physical appearance indicates that this may not be true.