When a child has leukaemia, control of blood cell production breaks down. The bone marrow - the soft tissue in the middle of our bones where all our blood cells are made - makes lots of abnormal white blood, or leukaemia cells. These never mature into proper white blood cells, vital to a healthy immune system, and so children with leukaemia are at more risk of infection.
Jenna Bradley, who was born with a rare form of cystic fibrosis, was diagnosed with leukaemia in August 2011 aged just three, after she had become very tired, pale and had developed a rash.
Read stories by others affected by blood cancer like Maria Macdonald who was diagnosed with non-Hodgkin lymphoma in 2003 at just 27.
Anyone can get a blood cancer at any age. Around 30,000 people, from babies to grandparents, are diagnosed with blood cancer every year in the UK.