Unless he has webbed penis (which can happen in intact boys), I would NOT worry about it. He's got a long, long way to go until puberty and the miracles of hormones! Webbed penis might be justification for surgery, but concealed penis might not be. I would just wait and see though.
http://www.drgreene.org/body.cfm?id=...detail&ref=916
http://www.drgreene.org/body.cfm?id=...detail&ref=916