In the field of early childhood research children's mobility is usually discussed only in terms of physical activity in the preschool yard. More seldom is it discussed in terms of mobility practices and how young children move in public spaces. With unique detailed video-ethnographic data on mobile preschools and a new combination of theories on space, mobilities and peer culture this article analyses how young children negotiate mobility practices and engage in embodied learning in the collective preschool routine of walking in line. Two empirical examples of walking in line in contrasting public spaces show how the mobile preschool group moves in space as a collective body co-produced by children's and teachers' individual bodies. It is argued that walks in line are not merely a form of 'transport' between places but are important as social and learning spaces. While walking in line, children collectively 'do' space in diverse ways depending on where and how they move, and in relation to where and when teachers negotiate safety issues. In this process, the spaces, activities and routines alike are transformed.