Many lower class urban neighbourhoods have long been characterised by an abundant street life where neighbouring mothers had coffee in front of their homes and a great number of children played in the street. An early 20th-century civilisation offensive changed the housing culture of the working classes so that residents drew a sharp line between public and private spaces. ‘Decent’ families were expected to live their lives indoors according to middle-class standards. City streets also changed and became spaces for car parking and motorised traffic. Families who could afford to left the city for suburbia. Those who stayed learned to see the public domain as a dangerous place that was better avoided. This paper, based on research conducted in Amsterdam and Rotterdam, argues that groups of middle-class families (called yupps: young urban professional parents) are challenging existing patterns in the city. First, by their staying in the city, and second, by their use of the sidewalk as a family place. In so doing, they transform the sidewalk from a formerly lower class to a ‘proper’ middle-class space. Colonising the sidewalk has become part of a new middle-class lifestyle.