Knock knees is an angular deformity of the legs in which the knees touch each other but the ankles are spread apart. This is also known as “genu valgum." Typically during childhood and especially during early grade school, knock knees is a normal part of growth. This is called “physiologic genu valgum."
During infancy and toddler years, bowlegs or genu varum is common. During the age of 18–24 months, the bowing improves and the legs appear more straight. Around the age of 2–3 years, parents may notice that the knees begin to touch presenting as knock knees. The most common age to see knock knees is around age 4. By the age of 7 or 8, there should be signs of improvement and straightening out.