If I still lived in New York, I'd be sorely tempted to chain myself to this bench. It doesn't seem like excluding some people from city property solely on the basis of their lack of children should even be legal.
UPDATE: To clarify: I am aware that the ban in question does not violate the federal constitution. That is why I said the policy in question should not be legal. I believe the city should be bound to open its parks to all unless there is some individualized reason why someone should not be granted entry, even if one can invent some circumstances in which it would be rational to ban childless persons. It is one thing to, say, affirmatively impose as a condition of parole restrictions on access to areas where children may gather, but something else entirely to impose a broad restriction on a class of people that is both over- and underinclusive and to deprive them of the equal enjoyment of public lands. (Besides, if you are concerned about pedophiles, shouldn't the more pressing issue be unaccompanied children? I'd venture to say that any given child in a park alone is more at risk than any given lone adult is a risk.)