It is unlawful for a person under the age of twenty-one years to work as an employee or otherwise in a retail, wholesale, or manufacturing liquor business or business establishment or for a person knowingly to employ another person under the age of twenty-one years in one of these businesses or business establishments. A person who violates this section is guilty of a misdemeanor and, upon conviction, must be punished as follows:
(a) for a first offense, by a fine of one hundred dollars or imprisonment for thirty days;
(b) for a second offense, by a fine of two hundred dollars or imprisonment for sixty days; and
(c) for a third or subsequent offense, by a fine of three hundred dollars or imprisonment for ninety days.