This double-blind, randomized, sham-controlled clinical trial will evaluate the effects of repetitive transcranial magnetic stimulation (rTMS) on children and adolescents with attention-deficit/hyperactivity disorder (ADHD) or autism spectrum disorder (ASD) and matched healthy controls. Participants aged 6-19 years will be assigned to active or sham rTMS protocols targeting the dorsolateral prefrontal cortex over 3 weeks, with assessment of changes in disorder-specific symptoms and cortical excitability. The study aims to determine the safety, feasibility, and preliminary efficacy of rTMS as a non-invasive neuromodulation approach in pediatric neurodevelopmental disorders.