Mobile Health Fitness Program for Adolescent and Young Adult Childhood Cancer Survivors

Inclusion Criteria: * Any diagnosis of cancer prior to age 21 * Off treatment for at least 6 months * For patients \< 18 years, parents must give informed consent and patient must give assent; patients \>= 18 must give informed consent Exclusion Criteria: * Any medical contraindication to exercise according to a physician or physician's designee * Non-English speaking * Current physical activity level exceeding Centers for Disease Control and Prevention (CDC) guidelines for activity (60 min of moderate-vigorous exercise/day for 5+ days/week (wk) including 3+ days of vigorous intensity activities and muscle-strengthening exercises on 3+ days/wk and bone strengthening exercises on 3+ days/wk for children \< 18 and 150 min of moderate vigorous exercise or 75 min of vigorous exercise/wk and 2+ days of muscle strengthening activities for adults \>= 18); the CDC guidelines are used to determine exercise prescription in our intervention; individuals already exceeding the guidelines would be unlikely to benefit from participating * Significant developmental delay per patient, parent, or physician report * Pregnant (per patient report); if participant becomes pregnant during the course of the study, she will be removed from further participation