Section 10. Any licensee permitting any minor to participate in the pari-mutuel or certificate system of wagering at a racing meeting held or conducted by such licensee shall be punished by a fine of not more than one hundred dollars. At least eighty-five per cent of the persons employed by a licensee at a racing meeting held or conducted by him shall be citizens of the commonwealth and shall have been such citizens for at least two years immediately prior to such employment.