Canada urgently requires a population health approach to children's mental health—promoting health and preventing disorders, in addition to providing treatment. Underpinning this approach, indicators could enable population monitoring, thereby informing ongoing public investments. To investigate potential indicators for British Columbia, we developed a comprehensive population health framework, established selection guidelines, reviewed data sources, and identified sample indicators. While 15 survey and administrative sources yielded 90 indicators, there were significant imbalances in coverage of the framework. To create truly comprehensive children's mental health indicators, we therefore recommend collecting new data, enhancing existing data sources, and evaluating existing programs.