A bruise on a child’s leg does not necessarily mean leukemia. If a child has a bruise on the leg, ask if there is a history of trauma or impact. If the bruise is localized due to trauma or impact, it does not require further treatment and will fade on its own over time. If the child has no trauma or impact, but has spontaneous bruising on the legs, preliminary blood work and coagulation tests should be performed. If the routine blood tests indicate thrombocytopenia, the bruising may be caused by thrombocytopenia, which can be caused by leukemia, aplastic anemia, or primary thrombocytopenia. If the child’s blood count is not abnormal, but the coagulation function is abnormal, the bruised leg is caused by abnormal coagulation function, and the child needs to consult the hematology department for further examination to clarify the diagnosis.