The paper objective is to know and understand the construction processes of the specialized field of knowledge and intervention that constituted child protection in the Americas throughout the twentieth century. The analysis is based on an ethnographic work in the archives of the Inter-American Children's Institute, specifically on a documental systematization from which it is possible to explore different versions of the preventative model that expanded in the region, and on which the «authorized voices» were raised to define certain childhoods as a model. The working hypothesis is that the ideologies of progress and development that influenced society's projects in that period had a specific impact on the construction and legitimization of such definitions.