Fatal Journeys Volume 4 focuses on a special theme – missing migrant children – given the growing number of children embarking on journeys that are dangerous and often fatal. Since 2014, IOM has documented more than 32,000 deaths and disappearances during the migration journey worldwide, although the true number of migrant fatalities is unknown, as many deaths go unrecorded. Data on deaths and disappearances of missing migrant children tend to be even more limited. According to IOM’s Missing Migrants Project, nearly 1,600 children have been reported dead or missing since 2014. This report discusses why it is often difficult to find data on missing migrants disaggregated by age. It explores what measures could be taken to improve data on missing migrant children, to help improve policy options and to prevent these tragedies from occurring. The report is a contribution to the joint efforts of UNICEF, UNHCR, IOM, Eurostat and OECD to improve data on migrant and refugee children. Without better data on missing migrants, any policy understanding of children’s migration journeys and the risks and vulnerabilities they face will remain incomplete.