One-quarter of the million migrants arriving by sea to Italy and Greece in 2015 were children: 94 per cent of those (235,500) arrived in Greece, of whom 10 per cent were unaccompanied. Of the 16,500 children who arrived in Italy, 72 per cent were unaccompanied. The number of children applying for asylum in Europe in 2016 was 10 times the same number in 2008. Children who migrate – be it alone or with family members – but do not seek asylum are unlikely to appear in official statistics. Existing estimates suggest that the number of children who arrived in Europe unaccompanied and did not seek asylum in 2013 may have been as high as the number of those who did apply for protection. Data on child migrants are crucial to identify and address their needs, but currently present serious limitations: there are gaps related to child migrants moving irregularly, risks of double-counting across countries or local administrations, and differences in definitions and methodologies used for data collection across European Union Member States, which hamper comparability. An estimated 10,000 unaccompanied children were missing in the European Union after having applied for asylum in a European Union Member State in 2016. It is unclear how many of these children may have ended up being exploited, or may have left their assigned guardians or facilities to join relatives elsewhere or find employment. More detailed, accessible and disaggregated data on child migrants, their profiles, reasons and intentions are necessary to ensure their protection, access to services and the fufilment of their best interest. An initiative is ongoing to include children in the global compact for safe, orderly and regular migration and the global compact on refugees.