There are many causes of nosebleeds in children aged 3-6 years, and leukemia is just one of them. If you have frequent nosebleeds, it is best to go to the hospital for a diagnosis. Leukemia is relatively rare, and in most cases, it may be due to fire, dryness of the nasal mucosa leading to fragile capillaries, and nosebleeds occurring as a result of external forces. Leukemia is a malignant clonal disease of hematopoietic stem cells that can manifest as nosebleeds, but nosebleeds are not a characteristic symptom of leukemia. If the nosebleed occurs frequently without touching, and at the same time it is not easy to stop, and the nasal mucosa is not broken because of inflammation, it is recommended to consult a doctor to determine the blood routine and coagulation tetrameter, and to check the bone marrow puncture to rule out blood diseases if necessary. If the nose bleeding is caused by fire or trauma, you can consider doing nasal endoscopy to observe whether there is dry mucosa or erosion of mucosa in the nasal cavity. In addition, if you find a swelling in the nasal cavity that is causing the bleeding, most commonly a hemangioma of the nasal cavity, you need to do a CT to make a definitive diagnosis and observe whether there is any destruction of the surrounding bone. Nosebleed if not often, parents do not need to worry too much, can let the child usually drink more water, eat more things containing vitamin C, to avoid bumping the nose to cause trauma bleeding.