"Yiiiiiikes, a kind gesture almost backfired dramatically. Certainly discourages owners giving kids a chance to sit in their dream cars!"
If the parent ask, I always say, "If your son/daughter knows how to respect a car of this caliper, yes they may."
or "If you have taught son/daughter how to respect a car of this caliper, yes they may." If you say that the parent usually tells the kid you get in just just sit still and don't touch anything, show the respect I taught you.
Most of the times it's the little boys that are just drooling but not touching, I ask them if they want to set in it and they do with great respect.
In the Vintage Race Car Club I belong to we encourage the youngsters to set in our racecars and the phone cameras are a clicking.
One time I was at Mid-Ohio Vintage Motorcycle Days with a Boss Hoss (SBC powered motorcycle) there was 8-10 year old boy just looking at the bike for 10 minutes.
I ask him if he wanted to set on it, he did and I shot his picture with his camera (film days) never thought much of it. About 3 months later I got call from his mom (she had gotten my number from one of the pictures a little boy took as the bike was for sale and had a sign). The call almost made me cry, it was all about how the boy's father had left them and she couldn't do the father/son things he needed, and he carried that picture of him on the motorcycle with him at all time as showed anybody who would look. She said they had to reprint it and the first one wore out.
Almost made me feel bad enough and want to drive to Ohio and take the kid bowling or something.
I tell that story to show a small gesture can make a difference greater than you imagine and may be worth the risk of an occasional scuff on your dash. JMO