Cavities form as a result of tooth decay. Tooth decay happens because of oral bacteria, which live naturally in your child’s mouth. Oral bacteria thrive on sugars. As they eat, they produce acids that eat away at the enamel of your child’s teeth. Regular brushing and flossing help prevent the cavity process. Infants and toddlers are at a unique risk for decay called Baby Bottle Tooth Decay or Nursing Caries. The common cause of decay is frequent, prolonged exposure to drinks that contain sugar, even breaskt milk. Tooth decay can occur when a baby is put to bed with a bottle or sippy cup.