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We reviewed longitudinal magnetic resonance imaging (MRI) studies exploring the brain development of children with attention-deficit/hyperactivity disorder (ADHD). Specifically, we conducted a systematic review of papers published until 9 September 2025 in English on pediatric patients with ADHD. After screening 3385 studies, 32 were selected for review. The age range at baseline for the participants in the review ranged from 4 to 18 years old. Children with ADHD exhibited delays in brain volume and cortical thickness compared to typically developing (TD) children, particularly at baseline, with these differences often persisting over time, with four key trends. First, children with ADHD showed smaller cerebral and cerebellar volumes, with no significant changes in their developmental trajectories. Second, there was a delayed peak in the cortical thickness, surface area, and gyrification observed in regions such as the prefrontal, temporal, and occipital gyri for children with ADHD. Third, the differences in brain volume and cortical thickness between ADHD and TD children diminished with age, particularly in the cerebellar white matter and caudate. Finally, ADHD children showed atypical growth patterns such as contraction of the ventral striatum surface area. A meta-analysis of longitudinal changes in total gray matter volume revealed no significant differences between children with ADHD and TD peers. Due to inconsistencies across studies and methodological challenges in integrating these findings, the results should be interpreted with caution. Selection bias is another concern. Multicenter studies with standardized protocols, long-term follow-ups, considering gender, comorbidities, and medication effects are required to enhance study replicability.