No - do not add your son's W-2 to your return. Your son is not required to file a return since his income falls below the filing requirements, but he could file his own return to get back any taxes withheld.
If you are using the online version of TurboTax, create another account for your son's return. Each return requires its own unique login and must be paid for separately (if the return doesn't qualify for Free Edition). If you prepare his return in your account, it will overwrite your return.
Please see the following TurboTax Help articles:
