This dissertation is a comparative study of children who succeeded as kings of England, Scotland, France, and Germany as boys under the age of fifteen in the central Middle Ages. Children are often disregarded in the historical record, even those divinely-ordained as king. The research undertaken in this thesis aims to uncover a more human aspect to medieval kingship by combining social aspects of childhood and gender studies with a political and legal approach to the study of the nature of rulership and royal administrative practices. Part I provides vital context of how royal fathers prepared their underage sons for kingship. I argue for the importance of maternal involvement in association, demonstrate the significant benefits a comparative approach brings to our understanding of anticipatory actions, and reveal the impact which changes in the circumstances and documentation of royal death had on preparations for child kingship. In Part II, I focus on vice-regal guardianship to expose how structural legal, social, political, and cultural changes affected the provisions for a child king. The symbolic meaning of knighthood, which had been a clear rite of passage to adulthood in the eleventh century, later became a precursor to kingship. The child’s progression to maturity was increasingly directed by legalistic ideas. These developments meant that, by the first half of the thirteenth century, queen mothers faced greater challenges to their involvement in royal governance alongside their sons. Part III presents a challenge to the idea that periods of child kingship were necessarily more violent than when an adult came to the throne through an analysis of instances of child kidnap, maternal exclusion from guardianship and departure from the kingdom, dynastic challenge, and opportunistic violence. Children often appear as passive actors controlled by the adults around them but accepting this unquestioningly is too simplistic. Child kings could make an impact on the political landscape even if they could not do so alone. Through an innovative comparative analysis of a child’s preparation for rulership, the care of king and kingdom, and the vulnerabilities and challenges of child kingship, I demonstrate far greater political continuity across medieval monarchies than is usually appreciated. This constitutes a fresh and original contribution towards the study of medieval rulership in northwestern Europe.