Violence is increasingly present in Quebec schools. Our position is that we should invest in "primary" prevention of violence by helping preschool children develop cognitive competencies. One of the aspects of cognitive development explored in this text regards children's Social Representations (SR) of violence. Indeed, a number of psychologists have demonstrated that SR serve to regulate behaviours in relation to social norms, and that a change in a person's SR influences her or his judgments and actions. This study consists of descriptions of children's SR of violence, and verifying whether these SR are stable or dynamic at ages of five and six years, and whether children are or are not stimulated by the Philosophy for Children approach used throughout one school year. Firstly, the results indicate that children's SR of violence can be grouped into four hierarchical perspectives. Secondly, the results indicate that the SR of children in the control groups hardly changed during the year, whereas those of children in the experimental groups showed a reorganization that was more marked. (Contains 8 tables.)