According to doctors at Columbia University Medical Center website, "Blount's disease is a rare growth disorder that affects children, causing the legs to bow outwards just below the knees. It is also know as tibia vara. A small amount of bowing is actually quite normal in young infants. However, as most children begin to walk, between the ages of 1 and 2 years old, their legs gradually straighten out.
In children with Blount's disease, the lower legs remain bowed or bow further outwards, which can lead to future problems with walking. Blount’s can be seen in a child less than 4 years of age as well as in early adolescents. "