No person shall purchase or acquire by gift, bargain, exchange, or in any other manner, the necessary books of instruction used or prescribed for the use and belonging to or in the possession, custody or control of any pupil, under the age of 21 years, regularly enrolled or attending any public school without first obtaining the authorization and consent, in writing, of the parents or guardian of said pupil or the principal of the school at which said pupil is regularly enrolled or in attendance, so to do.