As my opinion ,you may explain why your son was born

during the period of your first marriage still existed easily.First, it will take a long time to get divorce in USA throught the court; Second,if the CIS doubt if your second is real,you may take a DNA test between you,your wife & your son,& it to interviewer when you take your interview,the crossed test result
will win any doubt fot your marriage.
Good luck!