Background: Trauma adjustment varies in children and adolescents. Studies on objective risk factors of posttraumatic stress symptoms (PTSS) yielded inconsistent results. Dysfunctional posttraumatic cognitions (PTCs) might play a mediating role between risk factors and posttraumatic symptomatology. Objective: To investigate the interplay of the characteristics of the trauma (e.g. trauma type), the characteristics of the individual (e.g. age, sex), and the characteristics of the social environment (e.g. parental distress, marital status) on PTSS and depression, taking the child’s dysfunctional PTCs into account as a possible mediator. Method: Structural equation modelling was used to better understand trauma adjustment in two heterogeneous samples of children and adolescents: a sample of 114 participants aged 7–16 after accidental trauma and a sample of 113 participants aged 6–17 after interpersonal trauma. Results: In the accidental trauma sample, dysfunctional PTCs mediated the positive associations of younger age and lower parental educational level on child PTSS, but not on depression. In the interpersonal trauma sample, being female positively predicted child depression. Furthermore, parental dysfunctional PTCs positively predicted both child PTSS and depression. No mediation effect of child dysfunctional PTCs was found in the interpersonal trauma sample. Child dysfunctional PTCs moderately to strongly predicted child PTSS and depression in both trauma samples. Conclusions: The impact of the characteristics of the individual and the characteristics of the social environment on child PTSS and depression might depend on the type of trauma experienced. Dysfunctional PTCs mediated between the characteristics of the individual and the characteristics of the social environment and the severity of PTSS in the aftermath of accidental trauma, but not of interpersonal trauma. • Dysfunctional posttraumatic cognitions (PTCs) were associated with posttraumatic stress symptoms (PTSS) and depression.• In accidentally injured children, dysfunctional PTCs mediated between the characteristics of the individual and the characteristics of the social environment and the severity of PTSS.