The mole on the child’s arm is getting bigger and bigger, which may be related to physiological enlargement, external stimulation and cancerous transformation. 1. Physiological enlargement: if the size of the mole increases in proportion to the surface area of the skin of the body, it is a normal phenomenon, as the child grows up gradually, the mole on the body will also increase with the growth of the body. 2. External stimulation: If the child scratches the mole repeatedly, or the mole grows in the place where it is easy to be rubbed and stimulated, it may lead to the mole getting bigger and bigger. 3. Cancer: if the color of the nevus suddenly deepens, or its size suddenly increases within a short period of time, or satellite foci appear around it, or the surface of the nevus breaks down, the nevus may be a precancerous lesion, which needs to be diagnosed by taking pathological tissues and carrying out pathological examination. Parents are advised to bring their children to regular hospitals for consultation, clear diagnosis and standardized treatment by specialist physicians.