Would this ordinance be unconstitutional?

I think it would hold up as constitutional. Adults are excluded from certain children's play areas if not with a child. A zone around a school is similar. In general, there is no legitimate basis to give religious guidance to children whose parents havent sought or approved it. It is a coercive situation for a child. The guy is not just saying hello....he is exploiting a class of people who cannot protect themselves from his unwanted intrusion, and there is no first amendment right to target minors .