I think I would report them to CAS without mentioning anything. If you would say something and they wouldn't '"clean up their act" they would know it was you. I had a child show up a few years ago with a clear red hand print on their cheek. Mom (who was a constant drama queen) stated she was embarrassed to have left that mark - chuckle, chuckle. I said nothing as I knew she was too narcissitic to respond appropriately to what I had to say. I called CAS and learned from her "some awful person had called CAS " and had done some home visits. I also called to protect myself from anyone accusing me of having harmed the child. The same for your situation. Do you want the other parents to think your standards are so low you would find a dirty child acceptable? Turns out she had to go to parenting classes. She never knew it was me who called. Hope this helps.