Hi, I need to file my 2020 tax returns. My son dont have SSN (or ITIN). I am planning to apply SSN this month. What are the options for me to file tax returns by May 17th

To file by 17 May you can file your return and apply for an ITIN at the same time using one of the options in this link.  

However, you may be better to file an extension by 17 May to get an filing extension to 15 Oct, apply and obtain the SSN for your son and making him eligible for stimulus payments as your dependent with a valid social security number, then you can file your return by 15 Oct.  

To work the extension start your return, enter your personal information without your son on the return, put in your income and deductions and then go the "Other Tax Situations" tab.

Scroll down to "Other Tax Forms"

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"Start" the  "File an Extension" topic

If TurboTax is indicating you may owe taxes you can send in a payment with your extension to mitigate any late payment fees.