Section 20. No person, having a minor under his control, shall knowingly permit such minor to violate any provision of section nineteen or any provision of section thirty-four, nor shall any person procure or employ a minor to commit any such violation, nor shall any person, either for himself or as agent of any other person, furnish or sell to a minor any article the sale of which is permitted without a license by section seventeen, with knowledge that such minor would be selling such article in violation of section nineteen or in violation of section thirty-four, or after having received written notice to that effect from the school committee or any other officer charged with the enforcement of said section nineteen or said section thirty-four. Violation of this section shall be punished by a fine of not more than five hundred dollars or by imprisonment for not more than six months.