Contact with nature is vital for the development of children and teenagers. In the past, informal urban green spaces (IGS) such as vacant lots appear to have been used for such purposes. We need to better understand how previous generations used IGS to make sure young people today can also enjoy its social, mental, emotional and physical health benefits. This study quantitatively compared adult residents' memories of IGS use in their childhood and teenage years in two geographically and culturally distinct cities: Brisbane, Australia, and Sapporo, Japan. The results showed most respondents (>70%) remembered using IGS in the past, and preferred it over other green space because it was easily accessible. Most (>70%) recalled experiencing no problems (e.g. danger of injury) when using IGS, a contrast to recently increasing parental concern for children's safety. Such factors may limit present IGS use and prevent it from fulfilling the important role it played for previous generations' recreation.