Yes I went to an exhibition we 3yo DD yesterday - as soon as she was a few feet away from me she went up and touched a picture (luckily behind glass) because she wanted to show me something, I immediately sprinted over going "NO NO YOU'RE NOT ALLOWED TO TOUCH IT!" That's how they learn surely.
Oh but parents like these are probably the type who ban the word "no" from their household (I'm not exaggerating, I know parents like that)