Children interact with urban environments in different ways to adults in several ways, for example they tend to combine travel with play and they can learn from their experience interacting with the environment. Being out without adults present offers them the opportunity to gain skills such as way finding and making decisions about crossing the road safely. However they have less choice about where they go than adults do, because parents control many of their trips, and children are often not allowed to travel unescorted by an older person, so there tend to be interdependencies with other people’s travel. Since everyday travel and activities offers children the opportunity for physical activity, these restrictions have implications for their health. There have been a number of changes in the factors that influence children’s travel and outdoor behaviour in recent years, including the development of car-oriented lifestyles, increased numbers of mother in employment, and changes in attitudes towards children’s independent mobility. The purpose of this paper is to examine the nature of how children interact with the local environment, and the implications of this for their volumes of physical activity and so for their health, and how these have changed over time. The barriers that need to be overcome in order to encourage children to travel and play in ways that enhance their health will be considered. This paper will draw upon research carried out on projects carried out at the Centre for Transport Studies at University College London: /• ‘Reducing children’s car use’, in which the various surveys were carried out including questionnaire surveys of children and their parents and fitting a sample of children with accelerometers and asking them to keep diaries; /• CAPABLE (Children’s Activities, Perceptions and Behaviour in the Local Environment) in which children were also fitted with GPS (Global Positioning Satellite) monitors. Much of the emphasis was on looking at children’s independence; /• A comparative study of children’s independent movement in Britain, Denmark, Finland and Norway (led by the Transport Economics Institute in Oslo). // Trends in children’s travel and activity patterns and how they can influence their health will be considered briefly. Then the changes in the factors that influence children’s travel behaviour will be examined, including the growth in car use, changes in children’s activity patterns, changes in parental behaviour and attitudes, and the growth in home-based attractions. The ways in which these can be overcome will be considered in terms of lifestyles, lack of motivation and difficulties in making healthy trips. Conclusions will be drawn in terms of what is likely to encourage children to walk and cycle more and to be outside more, and which policies are likely to be successful. Conclusions will also be drawn about the forecasting methods used by transport planners in Britain and elsewhere with their emphasis on economic efficiency is biased towards car use. This makes getting children out of the car difficult; it is concluded that other overall objectives such as health and quality of life may be more appropriate than economic efficiency in transport planning.