If you use Online TurboTax, the son's return must be in a separate account (his own User ID). For future reference, when preparing multiple family returns, it may be more economical to purchase desktop software, which can prepare multiple returns. Depending on his situation, he may be able to use one of the two free products. I'll describe them in a separate posting that follows this one.
If you try to prepare a second return in the same account, it will overwrite your original return and make it unrecoverable.
The second return would need to be prepared in a separate account (separate User ID). You can use the same email address for notification purposes in up to 5 accounts, but each User ID has to be unique.
FAQ: How do I start another return in Online TurboTax?
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-onli...
