This study examined cognitive-motor interference (CMI) in children and adults by manipulating both cognitive and motor task difficulty during a dual-task paradigm (DT). Participants performed an auditory oddball task with three levels of cognitive demand while either sitting or walking on a treadmill, without instructions on task prioritization. Results revealed that increasing cognitive difficulty intensified CMI across all age groups, with younger children (7-9 years) showing the greatest decline in cognitive accuracy. Older children (10-12 years) and adults demonstrated more stable performance, reflecting the maturation of attentional control. Gait analysis indicated that spatiotemporal parameters improved with age, but treadmill use may have masked subtle developmental differences. Notably, cognitive load led to reduced gait variability and increased stability, suggesting adaptive resource allocation. Children prioritized motor stability under challenging conditions, while adults balanced cognitive and motor demands more effectively. These findings support a dynamic, developmentally-sensitive model of attentional capacity rather than a fixed resource-sharing framework. The results have practical implications for education and rehabilitation, highlighting the potential of targeted dualtask interventions to enhance CMI resilience in children. Overall, the study advances understanding of how cognitive and motor systems interact across development, emphasizing the importance of tailored strategies to optimize performance during critical periods of growth.