Wow... that's pretty bad! I have a friend who has a horse that has some screwd up legs but not THAT bad. It could be anything, but personally, I think he was born with it. You said the kid wants to do 4-H with him? Well, I do 4-H and if he's wanting to do like showing or riding, he can't with that horses legs... its also, like you said, really skinney, but I had two recsue horses that were in worse shape than that, and they pulled through with some montered feeding and special grain. In my oppion, that horse will probley never be able to be fixed, and the most he will ever be able to do is be pastured. With some seirous surgrey he might be fixed, but I don't really no, I would deffintaly call a vet.