3-year-old baby daytime is fine at night fever may be due to overdressing, hyperthyroidism and the presence of infections and other reasons. 1. wear too thick: night temperature is lower than the daytime, some parents have the habit of adding clothing to the baby at night, which is not conducive to the baby’s body heat dissipation. Coupled with the imperfect development of the thermoregulatory center of 3-year-old babies, it may lead to fever. 2. hyperthyroidism: this disease will accelerate the body’s metabolism, which can make the body’s oxygen consumption increased significantly, can cause low fever. 3. Presence of infection: When bacteria, viruses and other sources of infection are present in the baby’s body, the toxins released by these pathogenic microorganisms can cause fever. And these pathogenic microorganisms in the night activity is higher, may cause 3-year-old baby day nothing at night fever. There may be other reasons for a 3-year-old baby’s daytime fever at night, so it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy under the guidance of the doctor.