Two thoughts. I like the idea of putting something tacky on the end of the tape where they start to peal it off. Ever get pine sap on your hands? Tough to get off.
Another idea is a little more technical and costly, but is something I've thought of rigging up for my dumpster. Set a little motion sensor by the area which will only trigger on someone right on the bollard, and have a type of camera flash or strobe light turn on. This might make them think a picture is being taken and they'll stop. Of course, this may only be a preventative measure for a little while until they figure out it's fake.
You could put a camera there, but do you know who the parents are of the kid(s)? Even if you do, do you think those parents really even care?