Background The present study examines discrepancies between self‐ and adult‐perceptions of social competence in children with attention deficit‐hyperactivity disorder (ADHD), autism spectrum disorders (ASD) and possible co‐morbid disruptive behaviour disorders (DBD). Method Self‐reported questionnaires were collected from multiple informants at the baseline of a multi‐systemic family intervention programme for children (aged 5–12) with ADHD, ASD and possible co‐morbid DBD. In total, out of the 154 families eligible for the study, information was received concerning children from 124 families (children n = 121; mothers n = 117; fathers n = 86; teachers n = 97). In addition to this, a comparison community sample of 318 school‐aged children (approximately 10 years old) was utilized to examine the perceptions of children's social competence across intervention and population groups in more detail. Results Children's self‐perceptions in the prosocial dimension of social competence (i.e. cooperating skills, empathy) did not differ between the intervention and comparison groups. Interestingly, the children in the intervention sample expressed more impulsivity and disruptiveness – the antisocial dimension of social competence – when compared with the children in the comparison sample. Adult ratings demonstrated that mothers, fathers and teachers reported decreased prosocial behaviour and increased antisocial behaviour across overall dimensions and sub‐dimensions when compared with adults' ratings of elementary school children. Informant discrepancies between self‐ratings and adult ratings across intervention groups yielded significant effect sizes (eta‐squared) across all domains of social competence ranging from .09 to .25. Conclusion Children's positive self‐ratings of social competence relative to adult ratings increased within intervention sample when compared with population sample. The intervention sample children appeared to acknowledge their social competence deficits, yet self‐perceptions were inflated relative to adult ratings when focusing on peer relationship difficulties, particularly, aggression to peers.