This study explores the experiences of children and young people in Britain living through a serious family illness. The study considers the interplay between social structures, social relationships and individual agency. We draw on data from the Millennium Cohort Study to estimate the number of children and young people affected nationally and on seven in‐depth interviews to understand young people’s experiences and the effects on their daily lives. Living through a serious family illness impacts on young people’s educational achievements, mental health and social relationships over long periods. Policy and service responses are suggested.