Don't go back. It is very hard for your son to catch up with his studies in China. It seems like that you have a couple of choices here. It is not too bad at all. Why go back?
Trying to getting Canadian GC as a backup is a good idea while you are studying for a Ph.D. degree or working in U.S. It usually takes about 1.5 yrs to process Canadian immigration. However, please keep in mind that when your age is more than 44, your age score will be 2 points less.
If your J1 was supported by the Chinese government, it will be difficult to get J1 waiver.
Don't feel that you are too old.