Physical activity is fundamental to child health and development. Evidence suggests that environmental features may promote or hinder children’s participation in physical activity, in particular active transport and independent mobility. To date, a clear understanding of the relationships between environmental factors and children’s activity behaviors remains equivocal. An essential component of understanding children’s geographies and related outcomes is the ability to accurately assess the environments and environmental features that matter to children. Current measures include geographic information systems-derived features, audits, user perceptions (via surveys), and photographic data collection. An overview of these measures is provided, including discussion on strengths, weaknesses, and implications for research.