This Policy Insights relates some of the key findings from our report Measuring What Matters for Child Well-being and Policies, highlighting the need for better data on children's lives to inform the development of effective policies. It introduces a new framework for child well-being measurement that identifies which aspects of children's lives should be measured and how to best monitor child well-being. It also emphasises the importance of increasing the regularity and timeliness of data collection, improving data linking and combining techniques, and strengthening the capacity of data infrastructure to collect data on vulnerable groups of children.