Babies certainly need to clean their mouths. In infants, especially after drinking milk, the sugary substances in the milk can remain on the oral mucosa and tooth surface, which can be cleaned by drinking water and rinsing the mouth after milk or wiping the mouth with warm water. Infants are prone to thrush, bacterial stomatitis and other mucosal diseases, all of which are related to unclean oral cavity and are infections caused by fungi or bacteria. If the sugary substance in milk remains on the surface of teeth, it can produce acid for fermentation, which can also make the decay of milk teeth. Therefore, it is necessary to take care of the baby’s mouth, drink water regularly, and brush teeth when they erupt.