Knock-knee deformity is known as genu valgum in medical terms. It's very common in children ages three to five years old. In most cases, genu valgum corrects itself by age seven to eight. Very little improvement occurs after age eight years.
If the problem stays the same or gets worse, it may be caused by loose ligaments in the knee or weak quadriceps muscles along the front of the thigh. Being overweight or obese can make the problem worse.
Children with severe genu valgum have an awkward, lurching gait. Their knees may rub together when walking. Most do not run well and have a hard time in physical activities. These children seem clumsy and tend to fall more than normal.
The best thing to do is have your granddaughter's doctor take a look at her. Express your concerns based on your own experiences. There is some medical treatment for this problem. Most pediatricians wait until the child is at least five years old before doing anything about it.