The smart city has surfaced as pivotal in global discussions around unsustainable urban environments, but children as a social group, although constituting a major part of the global urban population, are surprisingly absent in these discussions. This chapter delves into the intersections of children’s mobility and sustainable urbanism by arguing that empirical studies of children’s everyday mobilities and practices are crucial for understanding and working towards ‘smart’ cities. The need to conceptualise mobility as an assemblage of human and non-human relations, of technologies and the material, is central in this enterprise. Conceptualising children’s mobilities as an assemblage is a fruitful way of approaching sustainable urbanism and smart cities, by providing a bottom-up approach where children’s (creative) practices take centre stage. Some findings from a two-year ethnographic project with children aged 7 to 13 and their parents from middle-class households in Sweden illustrate the creativity and playfulness of children’s everyday mobility practices. The author suggests that these everyday creative and playful mobility practices could provide a new framework for how to work towards ‘smart’ cities and sustainable urban environments.