Tooth Decay (Caries or Cavities) in Children Tooth decay first appears as white spots on the teeth. The cavity then turns a light brown color and progressively becomes darker. Teething A baby's first tooth usually appears between 5 and 7 months of age. Often, the two middle bottom teeth come through the gums first, followed by the middle four upper teeth. Periodontal Disease Periodontal diseases, also called gum diseases, are serious bacterial infections that destroy the gums and the surrounding tissues of the mouth. Thumb Sucking Thumb sucking is normal in infants and young children. It shouldn't cause any permanent problems if your child stops by age 5.