I will 'prolly get some guff back because of the consensus of many on this topic, but here goes:
When I was a kid I never think of defacing property however minimal or "non-permanent" it might be. If there is some sort of precedent to "child-art" such as this innocuous chalk expression I would never have done such an act without permission of the owners of the property be that property public or private. To assume one can deface property in the name of non-permanent art is rude and disrespectful.
Would any of the RV'ers allow some kid to use a dry erase marker (or some other non-permanent media) to perform her art on the side of your camper without permission. Should not matter since it is fun and creative. I am sure you would not allow it even if the rugrat did ask. Should not the same respect be given to the owners of the campground be that have public or private.
If permission is granted then have at it... be a juvenile Picasso!