Flat feet are common in toddlers as prior to walking the arch of the foot is yet to develop. As the child begins to walk shoes are not necessary indoors. Allowing the child to walk barefoot or with socks in a controlled environment will promote the gripping action of toes and will strengthen the muscles and ligaments that form the arch. Flat feet mostly always improve as feet strengthen. The development of the arch of the foot generally beings to settle by the age of 6. If you feel that the arch is still low and the child is complaining of pain, a review by a podiatrist is recommended.
Note: Outdoor on rough surfaces feet should be protected in lightweight, flexible footwear.