Chilhood cancers. Coloured scanning electron micrograph (SEM) of cells from the three cancers with the highest rates in children. Clockwise from top left are; leukaemia, lynphoma and brain cancer cells. These three cancers make up over 50% of all childhood cancers with leukaemia being the most common.Childhood cancer is rare, around 1, 600 new cases are diagnosed every year in the UK (in children aged 0 to 14 years). This means that around one child in 500 will develop some form of cancer by the age of 14 years.Childhood cancers account for 0.5 per cent of all cancers in the UK.