Red dots inside a four-year-old’s mouth may be caused by hand-foot-mouth disease, mouth ulcers and other diseases. 1. Hand, foot and mouth disease: this disease is mainly caused by enterovirus infection, usually through the respiratory tract or digestive tract and other ways of transmission, immunocompromised infants and young children is a common high-risk group, the child will appear tired, loss of appetite, abdominal pain and other symptoms, and the presence of millet-sized red papules or rashes on the oral mucosa. 2. Mouth ulcers: The cause of the disease is not yet clear, and may be related to heredity, unbalanced nutrition, excessive mental stress, physical injury, and decreased immunity. Typical symptoms are the presence of corn-like red spots at the mucous membrane of the tongue, lips, soft palate and other parts of the mouth, accompanied by pain. So four-year-old red dots inside the mouth may be caused by mouth ulcers. There are more causes for four-year-old red dots inside the mouth, you need to go to the hospital to improve the examination to clarify the specific causes.