Fever in children refers to when a child has a fever, the temperature is around 39.1-41℃. Fever lasting for more than two weeks is considered long-term fever. Normal body temperature in children is usually measured by rectal temperature of 36.5-37.5℃ and axillary temperature of 36-37℃. Under normal circumstances, axillary temperature is 0.2-0.5℃ lower than oral temperature (sublingual), and rectal temperature is about 0.5℃ higher than axillary temperature. If the axillary temperature exceeds 37.4℃, and the temperature fluctuates by more than 1℃ during the day, it can be considered a fever. The so-called low fever refers to an axillary temperature of 37.5℃-38℃, moderate fever of 38.1-39℃, high fever of 39.1-40℃, and hyperpyrexia of 41℃ or above.