No person under the age of 18 years shall be on or present in any public street, avenue, alley, park or any other public place in the City between the hours of 10:00 p.m. and 5:00 a.m. of the following day, official City time, unless there exists a reasonable necessity therefor. The fact that such juvenile is unaccompanied by any parent, guardian or other person having legal custody is found upon any street, alley or public place between the hours of 10:00 p.m. and 5:00 a.m. of the following day shall be prima facie evidence that such juvenile is there unlawfully and no reasonable excuse exists therefor. (See § 188-106. Exemptions)