hello thanks for consulting at hcm,,there are different types of stains,,such as extrinsic or intrinsic stains,,extrinisic is due to intake of different beverages-coffee,tea, etc,,i doubt these r causes in your little girl,,it could also be due to bacteria causes different color stains,, intrinsic causes are amelogenesis imperfecta,,flurosis, or tetracycline staining if mother has consumed it during teeth formation in the child,, it will cause brown staining,,later on when permanent dentition comes she can go in for bleaching or veneering of teeth,,either ways she is too young to undergo any treatment,, just to prevent caries she can take fluoride containing toothpaste once all the complement of teeth comes into oral cavity--deciduous teeth,, hope it helps,,take care..