Just tell them. I had to remind one of my dck's parent as he was stepping on my carpet! My carpet! I don't mind cleaning the floor which i do every day after they leave anyway but carpet it is not easy to clean the carpet and we do sit and play on it. So I told him "please don't step on the carpet as we sit and play there too. You can stay on the floor if you don't want to remove your shoes" he was apologetic and didn't do it again. I always believe if you don't tell others what/how you feel they wouldn't know.Just tell them simple.

Cocoon