BackgroundMany children and adolescents suffer from problematic levels of anxiety, but the multitude of these children do not receive an intervention. It is of importance to increase the accessibility and availability of child anxiety interventions, as to identify and treat anxious children early and successfully. Online platforms that include information, assessments and intervention can contribute to this goal. Interventions for child anxiety are frequently based on Cognitive Behavioral Therapy, because of its strong theoretical and empirical basis. However, the working mechanisms of Cognitive Behavioral Therapy in children are poorly studied. To our knowledge, mediation studies on child anxiety are non-existent regarding online Cognitive Behavioral Therapy.MethodsWe will aim at children aged 8–13 years with problematic anxiety. We recruit these children via the community setting, and refer them to our online platform ‘Learn to Dare!’ (in Dutch: ‘Leer te Durven!’), https://leertedurven.ou.nl, where information about child anxiety and our research is freely accessible. After an active informed consent procedure, the participants can access the screening procedure, which will select the children with problematic anxiety levels. Thereafter, these children will be randomized to an online intervention based on Cognitive Behavioral Therapy (n = 120) or to a waitlist control (WL, n = 120). The intervention consists of 8 sessions with minimal therapist support and contains psycho-education, exposure (based on inhibitory learning), cognitive restructuring and relapse prevention. Child anxiety symptoms and diagnoses, cognitions, avoidance behavior and level of abstract reasoning are measured. Assessments are the same for both groups and are performed before and after the proposed working mechanisms are offered during the intervention. A follow-up assessment takes place 3 months after the final session, after which children in the waitlist control group are offered to take part in the intervention.DiscussionThis protocol paper describes the development of the online platform ‘Learn to Dare!’, which includes information about child anxiety, the screening procedure, anxiety assessments, and the online intervention. We describe the development of the online intervention. Offering easy accessible interventions and providing insight into the working mechanisms of Cognitive Behavioral Therapy contributes to optimizing Cognitive Behavioral Therapy for anxious youth.