RecruitingBehavioural interventioniTONE Trial (exercIse Training in pulmONary hypertEnsion) Exercise Program for Pediatric PHChildren with pulmonary hypertension (PH) engage in less physical activity than their peers. This is a concern since adult data support exercise as a non-pharmacologic treatment for PH. Despite adult data, therapeutic exercise has not been widely adopted in pediatric PH. Investigators have previously demonstrated that children with PH have less skeletal muscle mass in association with worse exercise performance. Interventions to increase physical activity and skeletal muscle mass may improve exercise performance and quality of life in children with PH. This study will use wearable activity monitoring devices to promote physical activity in a 16-week pilot intervention in children and teenager with PH.