If you see a white substance that looks like milk sticking to the inside of your baby's mouth and tongue, he may have oral thrush. Oral thrush is not usually a worrisome disease, but it does need attention. It is caused by a yeast, Candida albicans, which is normally found in the mouth and intestines. If your child has been on certain antibiotics, for example, the yeast can overgrow and cause thrush. I will advice you see your doctor if Your child refuses to eat or The thrush lasts more than two weeks