Children with intellectual disabilities (IDs) show deficits in social information processing (SIP) that increased the risk of social maladjustment. As social inclusion is a major preoccupation for professionals and parents, it is important to know how foster SIP among these children, in order to support their understanding of social situations, their emotion regulation and social adjustment. The present study tested the efficacy of a new “SIP program for children”, considering specific strengths and weaknesses of these children. It also explored the potential causal contribution of SIP in elementary school children with ID to their emotion regulation, social adjustment and internalizing and externalizing behaviors. 30 children between 5 and 12 years with mild or moderate IDs, took part in a pre-test session involving measures on cognition and social problem solving. Teachers and/or parents completed questionnaires assessing children’s emotion regulation and social adjustment. Secondly, children were allocated to control or experimental groups. Experimental group participated in the “SIP program for children”. It was implemented by two trainers which used the specific material and technics described by the program during eight sessions to sub-groups of three children. After, all children took part in post-test sessions. Results showed significant improvement of social problem-solving abilities in children of experimental groups. After SIP training, they easily judged social behaviors and produced more complex justifications related to social consciousness and social rules, in comparison to the control group. Parents perceived children who had participated in the training as more socially adjusted and teachers described them as more integrated, autonomous and cooperative. These children were also perceived as displaying fewer internalizing problems.