RecruitingBehavioural interventionMobile App to Help Survivors of Childhood Cancer Navigate Long-Term Follow-Up CareThis clinical trial studies the effectiveness of a newly developed survivorship mobile application (app) designed for survivors, or their caregivers, of childhood cancer to help them better navigate long-term follow-up care. The survivorship app provides survivors access to their treatment history and follow-up recommendations, improves knowledge of their diagnosis, treatment, risks, and recommended follow-up care by using a message notification. The ability to quickly connect and establish care planning may enhance adherence to recommended follow-up.