How do i pull up both my previous year tax return and my son's previous year tax return? they are not on my file...only mine is.

Uhoh....did you use a different account and user ID for each return?  If you used the same account and user ID for both of them, the second one overwrote the first one and it is gone forever.  With online TurboTax you get ONE return per fee.

Or do you need to use the recovery tool to find the account you used for the other one

Many people have multiple TT accounts and forget how to access them.  Log out of the account you are in now.

Account recovery

https://myturbotax.intuit.com/account-recovery/

https://ttlc.intuit.com/questions/1901535-forgot-your-turbotax-user-id-or-password 

Or did you use the desktop version of TurboTax?  If so, the files are on your own hard drive or any backup device you used like a flash drive.

https://ttlc.intuit.com/questions/1901486-how-many-turbotax-accounts-do-i-have

https://ttlc.intuit.com/questions/1901535