Often you must look at your child's other symptoms to determine how serious the illness is. Although it may be scary when your child's temperature goes up, fever is not harmful. The average normal body temperature is about 98.6°F (37°C) .It usually rises during the day from a low of 97.4°F (36.3°C) in the morning to a high of 99.6°F (37.6°C) in the late afternoon.ften you must look at your child's other symptoms to determine how serious the illness is. Although it may be scary when your child's temperature goes up, fever is not harmful. The average normal body temperature is about 98.6°F (37°C) .