A three-year-old child with a sudden fever but no other symptoms is most likely to have an upper respiratory tract infection. Most of the upper respiratory tract infections are caused by viral infections, and the specific treatments are as follows:1. Oral medication: you can give your child oral medication to clear heat and remove toxins and antiviral medication, such as pediatric Bei Qiao Qing Fei Granules, pediatric Chai Gui Fever Relieving Granules, and Pudilan Anti-inflammatory Oral Liquid, etc. 2. Antipyretic treatment: if the temperature reaches over 38.5 ℃ or if there is a decrease in the level of comfort due to the fever, you can also give oral antipyretic medicine, and the antipyretic medication can be either Ibuprofen or acetaminophen. After taking antipyretics, you should give your child more warm water to make him sweat, which is conducive to cooling down. 3, visit the doctor for examination: if your child has recurrent fever, you should also be alert to whether there are other diseases, and if necessary, take your child to the hospital to do routine blood, C-reactive protein, chest X-ray and other related examinations, according to the cause of the examination, targeted treatment.