You don't add your sons W2 to your return. If he is required to file a return, he would file his own return. If would need to check that someone is claiming him on their return. If you are using the Online version, you would need to create a new account for his return. You should be able to use the Free Edition for him.
How do I add a dependent's W-2 to my return?------------------------------
How do I start another return in TurboTax Online?
