FWIW - My four year old daughter runs around naked lots during the summer...we all swim nude, and while we put on clothes afterwards (dh and I), she doesn't always. At her fourth birthday party, there were a bunch of nude kiddos running around the yard. I understand very well the dangers of molestation, but I do not want my daughters growing up afraid of their bodies...I want them to feel all the power their bodies have.
I have made it clear that you either wear undies to the store, or keep your dress down! (it's a pretty rare occurence to walk to the corner store without undies, but it has happened) We talk about no meaning no, why we can go nude some places and not others, etc. Mainly we chat about cultural differences, because she has noticed a difference in folks response to nudity, mostly through dh and I's responses to things. France, festivals etc. are places where people are more comfortable with their bodies and nudity, while my sister's suburb in Southern Cal. is not. All this "modesty" from our Puritan culture in the US is why so few women are comfortable nursing in public.
I'd mention the creep, then just move on. If he hung out all the time, I'd get more pushy...maybe keep talking to the guy, which would likely scare off a creep. We have a nearby, closeknit community park. I have also been talking with dd1 about trusting her intuition when she doesn't like someone. This has come up a few times for her (big kids wanting her to do something they would get in trouble for), and I share my thinking with her when it comes up for me...editted, of course. Read Protecting the Gift by Gavin DeBecker if you really want to know how to help protect your children.