Leukocytes are an indispensable group of cells that make up the blood and are widely found in tissues other than blood vessels and lymphatic vessels, as well as in the blood and lymph. Abnormal white blood cells in infants can lead to dangerous diseases such as leukemia, which can directly threaten the life of the infant. By knowing the normal infant white blood cell values, a mother can scientifically help her baby to detect abnormalities in white blood cells in time to prevent dangerous diseases from occurring. The normal value of white blood cells in infants varies with age, and the younger the age, the higher the value. The average within one month is less than 20×10^9/L, within one year is about 11×10^9/L, after 2 years old decreases year by year, to about 10 years old is close to adult. Specifically, the normal value of leukocytes in children is (5-12) × 10^9/L; in newborns it is (15-20) × 10^9/L. The causes of abnormal leukocytes in infants are: i. Pediatric leukocytosis The most common cause is granulocytosis, which is mainly due to bacterial infections, followed by fungal (also known as mycobacterial), viral, protozoal, and lickettsial infections. Non-suppurative inflammatory diseases (such as rheumatoid arthritis and other collagenous diseases), poisoning, hemorrhage, hemolysis, and other diseases that cause myeloproliferation are also most often associated with granulocytosis. In addition, physical and mental factors such as exercise, pain, panic, and rage can also cause granulocytosis. Pediatric leukocytes are particularly increased in five conditions: leukemia, leukemia-like reactions, extramedullary hematopoiesis due to various causes, infectious mononucleosis or infectious lymphocytosis, and severe bacterial infections. Second, pediatric eosinophilia The main cause is parasitic disease, followed by allergic diseases, including hookworm, filarial, schistosomal and ascaris larvae migration-induced allergic pneumonia, etc., can cause extreme eosinophilia, which can account for more than 80% of the total number of white blood cells. Urticaria, eczema, angioneurotic edema, asthma and scarlet fever are also common causes of eosinophilia. Third, pediatric lymphocytosis is mainly seen in whooping cough, tuberculosis, infectious lymphocytosis, infectious mononucleosis, and lymphocytic leukemia. Parents pay attention to their children’s white blood cell values in a timely manner, which can be of great help in understanding the disease.