My DD had a school friend to play this evening who has deliberately used a stamper (the ink pad type) on her pale pink duvet cover. They were playing in her bedroom, where her stamping set is stored in a box - to be brought downstairs and used on the kitchen table - my DD knows this and is usually very good. I only discovered the new pattern on her duvet cover after friend had been collected. Do I now say something to the mum, a good friend, or leave it ? I haven't yet tried to wash the duvet cover and am hoping it will wash out or at least fade, or it's spoilt. I'm cross at the situation, they are both 8 and ought to know better. I feel it's probably best left, but I would want to know if my DD had done it in another home.