The causes of red rash after fever in children include the following: 1. Symptoms caused by children suffering from early childhood emergency rash. If the child is relatively young, under 3 weeks of age, the fever at this time is mainly high fever, after 3-4 days of high fever, the child will have a small red rash all over the body, the mental state is relatively good, eating milk situation is also good. The fever subsides as the rash comes out, with the characteristics of a hot rash, and should be considered to be caused by early childhood emergency rash. 2. Symptoms caused by children with scarlet fever. The symptoms of fever, red rash and sore throat are caused by bacterial infection and can be treated with penicillin.