This article explores the enthusiastic reception with which many young Britons greeted the French Revolution. In some cases this sparked intense debate about the politics of family life, as children and youths sought to apply revolutionary principles of equality and democracy to their own lives. This was not an isolated phenomenon which sprang up simply in response to the revolution itself, however. Rather, it was the sharpest demonstration of what the article coins the ‘juvenile enlightenment’. The enlightenment has rarely been considered from the perspective of the child. This article argues that key features of the enlightenment had the potential to empower children and to encourage the articulation of distinct subjectivities. In places where this occurred in conjunction with other enlightenment practices, such as a vibrant urban culture with associated sociable activities, it could result in striking youthful engagement in a variety of civic and political affairs. The growing crystallisation of the category of ‘child’ was intrinsic to this process in some respects, but also significantly complicated it in others. Politicised young subjects might rebel against the constraints the subject position of ‘the child’ entailed, finding older more inclusive notions of ‘youth’ better conducive to political engagement. Examining these issues through the lens of a child’s manuscript diary enables close scrutiny of the shifting and complicated identities this context produced. More radically however, such an analysis reveals the extent to which juvenile subjects could themselves be significant political actors and actively contribute to the constitution of contemporary enlightenment culture.