As academic demands increase, school-aged children and adolescents often carry heavy backpacks, impacting their posture and musculoskeletal health. This study examines how backpack carriage affects children’s gait, focusing on the influence of waist strap design. In this study, twelve children underwent biomechanical tests while walking and running with and without backpacks, with weights adjusted based on daily habits. It can be found that waist strap-equipped backpacks significantly increased load response (F = 58.031, P < .001) and pre-swing phases (F = 58.031, P < .001) during both activities. In running, these backpacks also prolonged load response (F = 3.10, P = 0.004) and pre-swing phases (F = 3.10, P = 0.004). The study concludes that waist strap-equipped backpacks alter gait dynamics in children, affecting phases and contact times without impacting symmetry. This underscores the importance of waist straps in enhancing stability and reducing fatigue during backpack carriage.