Cavities in four-year-old children are usually caused by not brushing their teeth carefully, and need to be dealt with through fillings or root canal treatment, and usually pay attention to keep the teeth clean. 1. Permanent teeth usually erupt after the age of 6, so four-year-old children are milk teeth long cavity, for milk teeth long cavity, if the cavity is shallow, you need to use resin materials such as filling treatment; if the cavity is deeper, and even the emergence of pulpitis, etc., you need to under local anesthesia remove the pulp, root canal treatment. 2. It is important to note that children’s tooth decay is usually caused by long-term untimely cleaning of the oral cavity, parents should pay attention to help children develop a good habit of cleaning teeth. It is recommended that once parents find a four-year-old child with tooth decay, they should consult a doctor in a timely manner to improve the relevant examinations and standardize the treatment.