The general purpose of our work was to investigate, within a genealogical perspective (Foucault, 2006), the different sociocultural factors and aspects, which are present in the social construction of the phenomenon of poor children and the young who use Rio de Janeiro city streets as livelihood and/or dwellings. They are conceptually known as (homeless) children and young. The search for understanding the genealogy of this problem has led us to a historical investigation and, accordingly, the temporal constraint of the three last decades of the XIX century as the focus of our inquiry. The impossibility of transporting the current concept of homeless children and young back to that period of time has made us elect the categories of (loafer) and (vagrant). These categories were chosen for being possible to be investigated in historical documents and for the similarity and proximity of the social dynamics (individual-state-society) of the XXI century (homeless) population in Rio de Janeiro city. From this perspective, this study proposes to analyze the social construction of the notions of (loafers) and (vagrants) through our characters: children and young who were collected from the streets of Rio, in the end of the XIX century, accused of being (loafers) and (vagrants). From this urban context, we discuss under what aspects the idea of (progress) and (civilization), centered upon the social and urban order introduction, conform with the social construction of the notions of (loafers) and (vagrants). We also consider how the discourses and practices of the state and society get structured in the control and repression of these behaviors and ways of life, as they are perceived like expressions of vagrancy, bad habit and immorality ideas, bounded to poverty phenomenon and danger production. Our analysis also focus the way the necessity of the nation-state fabrication and the social experience of captivity - which meant in the real and abstract plans to produce a national identity and to conceive (modernity) - enrolled in the architecture of meanings which were present in the social construction of the notions of (loafer) and (vagrant). From this perspective, we describe the features of poor children and young who were collected from public places because of vagrancy in the last thirty years of the XIX century in Rio de Janeiro city. We also discuss the way the social construction of the notions of (loafer) and (vagrant), as being impregnated by a more general and abstract idea of incorrigible, typified in a state of behaviors or ways/means of life considered to be (abnormal) and dangerous, justifies the institutionalization of dehumanizing practices and discourses. Ultimately, we demonstrate the central role of the police in the institutionalization of discourses and practices destined to those poor ones regarded as dangerous. In addition, we build arguments which unveil horizons related to the historical process of assistance construction in the city of Rio de Janeiro.