: Children flatfoot is a frequent deformity in which there is a reduction in the medial longitudinal arch. Previous studies afford useful information about the prompt effects of foot insoles (FI). It is not clear if these effects long-lasting or might change over a longer period. The aim of this study was to investigate if wearing FI for a long time might change gait variables in children with flexible flat feet (FFF). Thirty Female children (9-13 years) with asymptomatic bilateral FFF were selected according to their arch index. Vicon 3D Gait analysis was used to calculate the kinetic variables (ankle, knee, and hip peak moments) during the gait cycle before and after 6 and 12- months period of wearing the FI. A significant decrease was achieved in terms of foot eversion and forefoot, knee and hip abduction and hip flexion peak moments after 6-months of wearing the FI. After 12-months, the previous parameters continued to decrease, in addition to significant increases were found in ankle dorsiflexion and forefoot adduction peak moments, and significant decreases were obtained in foot plantar-flexion and inversion, knee flexion, extension, and internal rotation and hip extension and internal rotation moments. It could be concluded that FI is feasible and effective in improving the lower limb kinetic parameters by achieving permanent changes in the young females with FFF when applied for successive 12 months.