In my first few years in business I had parents sending their children in nice white or pink clothing and I guess I have an evil streak because I would point them directly for the blackest mud possible. The parents learn quickly when you do that. Now I warn the parents every couple of months in my newsletter that clothing worn to daycare must stand up to mud, all creative mediums and all food because we have FUN!
I do insist that splashpants are left at the daycare all year round which helps protect them but you can't use those when it gets too hot.