How can I renew my sons visa from USA when he is still in china?

I recently married a Chinese woman who has a child from a previous marriage well my wife finally got her temporary citizenship and has been in the country almost 2 years and we have been trying to get our son here now his passport has only 7 months left and they won't issue a visa for him unless he has at least 8 months left on his passport do we have to go back to china to renew or can we do it from here?