The case for children and young people’s involvement in health research has been well documented, but less attention has been paid to the experiences and impact of involving children and young people rather than adults. This paper explores these issues in relation to a project undertaken for the James Lind Initiative on the availability, quality and reliability of existing data on young people’s involvement in studies supported by the National Institute for Health Research (NIHR). The project found that there was no systematic way of getting reliable and comparable information about which young people are involved in health research in England, what form that involvement may have taken or the impacts of involvement. There is a need to better collate and disseminate evidence on young people’s involvement in research, using both existing systems and processes, and the possible development of new metrics and measures. Not having this information risks children and young people’s involvement continuing to develop in a piecemeal fashion. Further research is needed about how, when and where children and young people are involved in health research, and about the impact of involvement on research and on the children and young people involved.