A surge of investment in Europe, North America and Australasia on children's and school travel planning has highlighted problems of the built, social and policy environment as barriers to children's active transport and independent mobility. Many aspects of the built environment can influence children's active transport, physical activity and health, including excessive trip distances, footpath provision, traffic volumes and speeds and road crossings. Research on the built environment often uses measures of neighbourhood 'walkability' that draw on these barriers/enablers, to allow planners and other actors to understand differences in the potential of built environments to support active transport. However, these measures and indices are usually derived from studies of adult, not child, travel behaviour. This paper summarises recent attempts to develop environmental measures and indices based on children's travel behaviour. It highlights their advances and limitations, and identifies possible ways forward. A new set of measures is outlined, drawn from the literature, which build upon and improve recent practice. Geographic information systems (GIS) are used to transform these measures into a composite walkability index for neighbourhood environments that more accurately reflect children's active travel potential. The method is applied to a school neighbourhood in Brisbane to demonstrate the approach. Refinements and practical applications for the method are advanced. A comparative study currently using the method to help explore built environment influences on children's independent mobility is noted. The method provides the potential for more nuanced and targeted research into children's travel and school travel planning, and for improved transport and land use planning interventions targeting travel behaviour change and children's health.