The dreaded "W" sit.

There is some debate over whether that causes the hip/leg angles to be funny, or whether kids with funny hip angles find that a comfy way to sit.
I think the latter option is more like it. My 6'7" husband has extreme knock-knees. If he puts his knees together, there are 5 inches between his ankles. The doctors told him in his teens it was because he grew so fast between his junior and senior years. However, our son is developing many of the same body traits as my husband (long bones in the limbs, which have just become apparent since the onset of puberty). His knees are growing in the same direction as DH's. Son is only 5'4" at 13-next-month and is not growing very fast at all. So I think the doctors were just clueless.

Karen