did you son stayed with you on year 2004.
you can use 3 years time to determine the resident status.
ex. 2003 --- 100 days
ex 2004 --- 100 days
ex 2005 --- 150 days
then under the above days of calcuation . you son can be a residents.
apply the ITNI number, no matter what happen.
also , if you are Canadian or Mexcian, you can claim residence -with no problem.