This book delves into the past and examines the origins of activism against child labour. It addresses a hitherto under-examined question: how and why did child labour develop into a key concern between the 1880s and 1930s? Who were the protagonists who first raised the issue of child labour as a global concern? The study aims to provide the first account of the history of diverse and locally grounded – but nationally and frequently globally connected – child labour opponents in the Americas, their motivations and campaigns, at the turn of the 20th century. I argue that, for the period between 1888 and 1938, one can identify similar protagonists, a joint goal, a broadly similar timing, common platforms, comparable campaigning mechanisms and many types of connections or entanglements across regions. Nevertheless, in contrast to the global anti-slavery movement, child labour opponents formed a loosely institutionalised network which lacked an international organisation that focused specifically on child labour. A global history approach to child labour opponents helps reveal large-scale patterns across societies and highlight similarities and differences between cases.