Occasional fever in a three-year-old baby, infectious factors such as viral, bacterial, mycoplasma infections, and non-infectious factors such as leukemia, connective tissue disease, etc., are analyzed as follows: 1. Infectious factors: if the baby’s body is infected by bacteria, viruses, mycoplasma, chlamydia and other factors, there will be occasional fever, which may also be accompanied by a runny nose, sneezing and other phenomena. 2. non-infectious factors: leukemia, connective tissue disease and other diseases may also cause occasional fever. Occasional fever in three-year-old babies may also have other causes, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.