A high blood lymphocyte count in children may be a normal physiologic increase, or it may be caused by viral infection or tuberculosis. 1. Physiological increase: If the blood lymphocyte count of children is high, only slightly high, and not accompanied by other discomforts, it may be a normal phenomenon, caused by individual differences, and can be observed. 2. Viral infection: this is one of the most common causes of high blood lymphocyte counts in children, which may not necessarily have symptoms, but some children may have symptoms of viral infections, such as fever, cough, diarrhea and so on. 3. Tuberculosis: It is also one of the most important causes of high lymphocyte count. Children infected with tuberculosis will have a high blood lymphocyte count, which may be accompanied by coughing and sputum. There are other reasons for high blood lymphocyte counts in children, which need to be judged together with symptoms and signs. It is recommended to consult a doctor to find out the cause of the high blood lymphocyte count and to cooperate with the doctor for treatment if necessary.