Minors under the age of eighteen (18) years shall under no circumstances frequent, loiter, go or remain in any massage establishment licensed hereunder at any time, unless it be upon some lawful errand and sent under the direction, and the consent and knowledge of the parent, guardian or other person having lawful custody of such minor. It shall be unlawful for the proprietor of any establishment so licensed to allow or permit any such minor to frequent, loiter, or remain within the hall in violation of this section.