Leukaemia is cancer of the blood. It is the most common form of cancer in the childhood. The cancer cells grow in bone marrow and goes into the blood. Our bone marrow is the soft, spongy and considered as centre of some bones. It makes blood cells. When a child is said to have Leukaemia, the bone marrow makes abnormal blood cells that don’t mature. The abnormal cells are usually the white blood cells also called leukocytes. The bone marrow also makes a fewer healthy cells. The abnormal cells reproduces very quickly and they don’t work as same as the healthy cells. The types of blood cells involve Red blood cells (Erythrocytes), Platelets (Thrombocytes), White blood cells (Leukocytes). The exact cause of the disease Leukaemia in children is not actually known. There are certain conditions inherited on from the parents to children that increase the risk for the childhood Leukaemia. But mostly childhood Leukaemia is not inherited and is found the changes or mutations in genes of the bone marrow cells. These changes may occur early in the child's life or even before their birth and may even occur by chance (sporadic).