[Tommy]

What follows is not advice. It is merely what I do.
When I arrive where I suspect naive people may get too close (e.g., a cruise-in), I set up my folding chair nearby and monitor things until the sidepipes have cooled enough to not be dangerous. Sooner or later I'll wander off to register or see the other cars. If some moron lets their unruly child scratch my car or leave sticky handprints on it, that's the price I pay for bringing my car to a public place and leaving it unguarded. Should they know better? Yes. But as I know some will be irresponsible, the ultimate decision to participate or not is mine. ... BTW, I routinely allow well behaved children to sit in my car.