This article draws on interdisciplinary social science to explore the socio-legal classification of children as `offenders' and `non-offenders'. It applies classification theories interpretively using two case studies from the USA and Scotland. It is argued that such classifications oversimplify complex issues and, in reality, children move between categories over time. Classifications contribute to the ascendancy of certain aspects of children's functioning over others. Their use risks that we stop seeing the individual child. The `borderline' or `hard cases' (persistent and/or serious offenders) highlight the variability of judgement. These cases illustrate the moral dimension of classification whereby some children come to be treated as adults in justice systems.