Lab. Code, § 1304

Failure to produce any permit or certificate either to work or to employ is prima facie evidence of the illegal employment of any minor whose permit or certificate is not produced. Proof that any person was the manager or superintendent of any place of employment subject to this chapter at the time any minor is alleged to have been employed therein in violation of this chapter, is prima facie evidence that the person employed, or permitted the minor to work. The sworn statement of the Labor Commissioner or his deputy or agents as to the age of any child affected by this chapter is prima facie evidence of the age of the child.