If you file your return before you get the child's SSN you will not be able to get EIC---so wait until you have the SSN.    The PATH act says that you cannot get child related credits by amending to add a child's SSN.   The SSN has to be on the original tax return.  

You can still e-file a 2020 return until October 15, 2021; after that you have to print, sign and mail it because e-filing will close down.

You need that SSN for the child tax credit, too---so wait.

https://ttlc.intuit.com/questions/1899157-what-are-the-qualifications-for-the-earned-income-credit-e...

https://www.irs.gov/credits-deductions/individuals/earned-income-tax-credit/use-the-eitc-assistant

And.....the $18,500 is your standard deduction for filing as HOH.   If you have income earned from working, even if it is below that amount, you can still get some EIC if you have a qualified dependent.

The previous answer is not quite correct. You must file a “on time“ return that contains the child’s Social Security number, in order to qualify for EIC.  Your return will still be considered on time if you applied for the automatic extension before May 17.  In that case, you have until October 15 to file an “on-time” return.

However, if you did not apply for the extension, your return will not be considered on time and you will not receive EIC for your child for 2020, even if you include them as a dependent with a Social Security number.