My son will want to leave China at some future date, how difficult will it prove to be?

My son is on assignment in China working for an American based company. The company has a Chinese manufacturing facility set up with almost all local labor needs filled by qualified Chinese. The duration of his assignment is fluid. He is an American citizen and has met and married a young Chinese woman, I recently learned she is pregnant, which makes us very happy. At some point down the road, they are going to want to come back to the states to live. What should we being doing now to make this future transition go as smoothly as possible. Can we get started with the necessary forms, documents, legal requirements, etc., etc., etc.,. What does my son need to get started on from his end, and from our end?? Do we need to line up any legal assistance or ??
Thanks for any help you can provide----------Ben DeLozier