Research into young children's understanding of bullying in the early years of schooling is limited. The current study examined young children's understanding, explanations and reasoning behind whether behaviours represented in cartoon scenarios depicted bullying or non-bullying incidents. Seventy-seven children aged 4-8 years from one kindergarten and three schools in metropolitan South Australia participated in single, age-appropriate interviews with an early childhood educator/researcher. All children described each cartoon (N = 77) explaining their reasons why they considered each one as bullying or not (N = 76). Consistent with previous research which employed cartoon methodology with young children, findings indicated that children confused bullying with aggressive-only behaviour, resulting in over-labelling incidents as bullying. Examination of their thinking about bullying revealed that children in this study drew on moral reasoning perspectives and their understanding of relevant behavioural and social expectations and conventions.