Breathing tobacco smoke is linked to poor health in young children, with their homes identified as the primary place of exposure. This UK study uses focus group discussions to explore how mothers living in disadvantaged areas use space within their homes to smoke while looking after children aged 0-4 years, and critically examines how they define non-smoking or smoking homes. Many women imposed temporary and ad hoc restrictions, and this research highlights how the mothers' desire to create a smoke-free environment for their children competes with their caring responsibilities, and how their efforts are restricted by the limitations of the physical environment of their homes.