Flat feet are common in toddlers because the arch of the foot has not yet developed before walking. As children begin to walk, the arch typically develops and strengthens over time.
Allowing a child to walk barefoot or with socks (indoors in a controlled environment) promotes toe gripping and helps strengthen the muscles and ligaments that form the arch. Flat feet most often improve as feet strengthen, and arch development generally settles by about age 6.
If the arch still appears low and your child is complaining of foot pain, a review by a podiatrist is recommended.