The purpose of this study was to examine, in a sample of residential care children in Quebec, Canada, the moderating role of cognitive flexibility in the association between maltreatment and emotion regulation competencies. The sample included 69 children aged 8 to 12 and their group home educator as their primary caretaker. Educators completed questionnaires evaluating child emotion regulation competencies and cognitive flexibility. Child history of maltreatment and sociodemographic data were collected on the basis of the children’s child protective services files. Moderation analyses showed that the effect of child maltreatment on emotion regulation was only present for children with high levels of cognitive flexibility, such that the less children experienced severe maltreatment, the more they showed emotion regulation competencies. Children with low cognitive flexibility displayed lower levels of emotion regulation regardless of their maltreatment history. These results suggest that focusing on cognitive flexibility when intervening with children in residential care could help strengthen their emotion regulation competencies, which may prevent further maladaptive behaviors.