Knock knees (genu valgum) means that a particular person has a large gap between his feet when he is standing with his knees together. I have seen many children have knock knees, which is obvious in and around the age of 4 years. Knock knee usually doesn't cause any problem but it may cause knee pain and difficulty in walking. In maximum cases, knock knees don't need to be treated because the problem tends to correct itself as a child grows. If it persist joto adulthood and causing problems, such as knee pain, one should have to identify the root cause of this knock knee. Rickets may cause knock knee and tickets can be treated with vitamin D and calcium supplements.