Apply for Social Security Number for your son since

he is an American citizen. You can use it for tax return. No matter how many jobs you had last year, add all the salary together according to the W-7(I can't remember exactly. It's a statement from your employer stating exactly how much you earned last year and how much taxes were withheld. It's usually sent out at the end of January. You should get two statements from your employers. I believe you may choose to file as a resident or nonresident. I chose filing as a resident since it will help with your immigration later. This is just my experience but I am not a tax expert. So wait for other professionals too.