I think all along my girl has had milk residue but has been treated for thrush. She doesn't have anything on her tongue, just spot spots on her cheek and inside lip. While sleeping I rubbed with a warm towel and it came off. It's hard to get inside her cheeks b/c she's 14 months, but why would she have milk residue? She nurses and get some cow's milk, along with water and diluted cranberry juice.