The slippery slope aspect bothers me, but I think more than anything, this a great test case for the police to point to to prove they aren't profiling in enforcing this rule. If the police limited enforcement of this rule to individuals who fit the profile of most pedophiles (male), it would eventually be overturned in court as discriminatory.
At the park that I go to most often, the prime benches with the most shade (this is south Texas, after all) are nearest to the playground. If one were tired out from walking/jogging/running/biking around the park, those benches would be the best place to sit. This would be an unfair rule in that instance.