Background Characteristics of preschool and child care centres have previously been shown to be associated with children's health behaviours such as physical activity and screen-based sedentary behaviour. This paper investigates differences in physical environments, policies and practices between child care centres in Melbourne, Australia and Kingston, Canada which may be associated with such behaviours. Methods Audits of child care centres were undertaken by trained research assistants for the Healthy Active Preschool and Primary Years (Melbourne, Australia; n = 136) study and the Healthy Living Habits in Pre-School Children (Kingston, Canada; n = 46) study. Twenty-one of the audit items (nine physical environment; 12 policies and practices) were assessed in both samples. Example items included outdoor play and shaded areas, availability of equipment, physical activity instruction for children and staff, opportunities to use electronic media and staff/child interaction during physical activity time. Analyses were completed using SAS version 9.2. Results Compared with Australian centres, a higher per cent of Canadian centres had a formal physical activity policy, reported children sat more frequently for 30 min or more and allowed children to watch television. A higher per cent of Australian centres provided an indoor area for physical activity, shade outdoors and physical activity education to staff. Children in Australian centres had access to more fixed play equipment and spent more time outdoors than in Canadian centres. Conclusions These findings may help inform the development of best practice and policy guidelines to enhance opportunities for healthy levels of physical activity and screen-based sedentary behaviour within child care centres in both countries. (author abstract)