Saw a pre-schooler wandering around a car park area in Philly's Fairmount Park three years ago. Kid was running in and out between the cars as we were loading bikes and getting ready to leave. Told the other group of adults in the park area to keep an eye on "their" child, and was told it wasn't their child, they had no idea who or where the parents were. ! I can't remember if we drove off or if we did see the parents return. (Now with my own kid, I'd offer to help the kid find his/her parents.)