Can I file for my son?

Yes, that is fine. If you are claiming his as a dependent on your return you will need to make sure that you indicate that he can and will be claimed as a dependent on someone else's return. You will do that in the Personal Info section of his return.  

Did you use Turbo Tax for your return?  Don't use your account.

Online is only good for 1 return.  But you can use the same email address for 5 accounts.   How to start another return in the Online version      https://ttlc.intuit.com/replies/3288574