Ricket may result from lack of vitamin D or other factors.

There are a number of different causes of knock knee (genu valgus deformity) .One cause is physiological which means its a normal extreme variant which usually will correct as the child grows older usually seen from ages 2 to 5. This usually is symmetrical ( both sides affected and similar in curvature) its not usually an extreme amount of bend. It tends to run in families
also.

Another common cause is rickets which results from bone weakness from calcium metabolism disorder.
Other less common causes include bone growth disorders and injury and infections to growth areas of the bone.
The treatment is directed to cause, physiological k leg deformity requires no real treatment, but monitoring, as it will resolve. The other causes have their own treatment criteria.
In summary knock knees can be a normal variants or from bone abnormalities. It is advisable to see a doctor who can recognise the specific cause and treat appropriately.

An orthopaedic surgeon should make right diagnosis.

Right foot wares important too.