Abnormal white blood cells that spread out to the skin may lead to tiny, dark, rash-like spots appearing. This group of cells under the skin is called granulocytic sarcoma or chlorma. Although this is rare, but it can be a sign of childhood leukemia.
Bruising and bleeding which characterize leukemia may also cause the appearance of small spots called petechiae. These might seem like a rash, too. Therefore, it is difficult to differentiate between petechiae and bruising caused by other causes and leukemia. A medical history, physical examination, and imaging tests will be the best combination to rule out childhood leukemia.