The justice of criminal punishment depends in part on the possibility of holding people accountable for their choices. There is a wide variation between nations on the age at which juveniles can be prosecuted in adult criminal courts. This variation reflects disagreement about the underlying logic of responsibility. This paper examines the philosophical difference between adults and children as agents. The paper argues that the moral status of children is importantly distinct from adults, specifically with respect to how responsibility should (...) be mitigated. The paper explains this in terms of the developmental aspect of childhood. By considering empirical evidence from psychology and neuroscience we can understand the mistakes that juveniles make as a form of developmental impairment. The paper shows why these findings lead to the conclusion that the practice of trying children as adults is immoral and should be eliminated. (shrink)