Children’s social competence has been largely assessed using informant reports, yet few studies have explored how these ratings reflect real life behaviours, and how maternal childhood characteristics influence the latter. In the present study, children between 9- and 13-years-old were observed discussing a source of conflict with their mothers. Children’s engagement in behaviours classified as socially competent (e.g., smiling, cooperating) and incompetent (e.g., interrupting, confronting) during the discussion were coded. The associations between children’s observed social competence and informant ratings of children’s social competence were examined. Informants were children’s mothers, teachers, and themselves. In addition, maternal childhood characteristics (i.e., aggression, social withdrawal, likeability) and their associations with children’s social competence were explored in a sub-sample of participants. Results indicated that mothers’ ratings of children’s social incompetence as well as higher levels of maternal childhood aggression or social withdrawal predicted less child engagement in socially competent behaviours. Teachers’ ratings of children’s social incompetence predicted greater child engagement in socially incompetent behaviours. Furthermore, higher levels of maternal childhood aggression were associated with children’s greater use of socially incompetent behaviours for mothers low in childhood likeability, and children’s lesser use of socially incompetent behaviours for mothers high in childhood likeability. Results from this study take a first step in investigating how informant reports reflect children’s engagement in specific socially competent and incompetent behaviours within a naturalistic interaction. Moreover, our results contribute to the literature on maternal childhood histories and the intergenerational transfer of risk.