Background: Traumatizing events put children at risk of developing severe mental health problems. There is a large gap between the need for and access to evidence-based treatments for traumatized children and youth. To bridge this gap, the treatment model stepped care trauma-focused cognitive behavioural therapy (stepped care TF-CBT) has been developed. The model consists of a parent-led therapist assisted component (step one), with an option to step up non-responders to standard therapist-led TF-CBT treatment (step two). We will investigate the feasibility, acceptability, outcomes and predictors of an adapted stepped care TF-CBT model, where step one is placed in the first-line municipal health services and step two in the second-line specialist health services. We will include the perspectives of children, caregivers, therapists and service leaders. Methods: This is a multicentre feasibility study, with a mixed methods longitudinal research design. We recruited 45 therapists across 19 municipalities in Norway and provided training in the stepped care TF-CBT model. Through the therapists, an estimated 78-83 child-caregiver dyads will be recruited. The main criteria for inclusion are age 7-12 years, at least moderate post-traumatic stress symptoms following exposure to trauma, and that receiving parent-led treatment is safe for the child. Interviews to explore experiences with the model will be conducted with children, caregivers, therapists and municipal service leaders. Further data from children, caregivers and therapists will be collected throughout treatment and at 3-month follow-up to assess post-traumatic stress symptoms and mental health, daily functioning, quality of life and therapeutic alliance. Discussion: The results will help inform clinicians and policymakers of the potential benefits and barriers of providing step one of stepped care TF-CBT in a first-line setting. The study will increase knowledge of factors that characterize children and families that benefit from the parent-led step one, and families that may need modifications in the model, or different interventions.Trial registration: ClinicalTrials.gov, NCT04073862. Retrospectively registered 03 June 2019 (first patient recruited May 2019), https://clinicaltrials.gov/ct2/show/NCT04073862