Wis. Stat. § 103.76
Whenever in any proceeding in any court under any of the labor laws or under ch. 102 there is any doubt of the age of a minor or as to whether an individual is a minor, a permit authorizing the employment of the minor issued under s. 103.70 or an age certificate issued under s. 103.75 shall be conclusive evidence. In the absence of such permit or certificate, a birth certificate, a verified baptismal certificate, a valid operator's license issued under ch. 343 that contains the photograph of the license holder, or an identification card issued under s. 343.50 shall be produced and filed with the court. Upon proof that the birth certificate, baptismal certificate, operator's license or identification card cannot be secured, the record of age stated in the first school enrollment of the child shall be admissible as evidence of age.
Wis. Stat. § 103.76