Children begin to walk anywhere between eight and 18 months of age. For the first two years, your child's feet will seem to have fallen arches. Flat feet are normal in a young child due to weak muscle tone in the foot, a generous padding of fat, and loose ankle ligaments that permit the foot to lean inwards. As your child masters walking, the ligaments and muscles will strengthen and the fat pads in the arch area won't be so noticeable. By around five years of age, your child should have normal arches in both feet.