Alot of times, they just have residual milk on their tongue, but, if it looks like a coating and there are white specks on the inside of their cheeks, it is probably thrush. I usually recommend making up a Bayberry tea, then put it in a spray bottle and spritz the baby's mouth with it. If the child is nursing, I would also have the mother drink the tea to help flush out any yeast they might be passing back and forth.