You said that underage persons can work at licensed premises. Does this mean any age?
No. They must be over age 14. Children over the age of 12 may work under the direct supervision of their parent or guardian in connection with the parent's or guardian's licensed premises. In addition, they must not be serving, selling, dispensing, or giving away alcohol beverages unless they are at least 18 years of age. If over age 18 and they do not have their own operator's license, they must be under immediate supervision by the licensee, agent, adult member of the licensee's immediate family (a person living in the same household), or a person with an operator's license. (Secs. 125.32(2) & 125.68(2), Wis. Stats)
https://www.revenue.wi.gov/Pages/FAQS/ise-atundrg.aspx