That's his knee... Genu Valgum can be from different causes but if it's skeletal then the boys bones are acually alined such that he couldn't possibly get the ankles together and stad up. If it's not congenetial then in lying you may be able to bring the ankles together without too much pressure at the knee, in which case his weight has caused the position and the medial knee will be very lax, he will also grow into this position and as the surgeon says it is imperitive he loose weight so as not to worsen this condition. He very likely lacks the muscular control to keep his leg straight and as such may need strengthening exercises... which may be very very hard for him to do given his age. I suggest telling the parents that his weight will worsen the genu valgum - this is true. See Heuter Volkmann law (Answers.com - What is the heuter-volkmann law) which basically says if asymmetrical load is going onto a growing bone then it will grow assymetrically and in this case only cause worsening of the genu valgum. He may need corrective surgery in the coming years, but he is very young now and has lots of growth left to do. He needs to loose weight and likely needs to get some more strength in the legs.