My son is an American citizen born abroad in 2017. I didn't get his EIP 1,2, and 3 because he didn't have a SSN. But I recently got his SSN last month.
I can claim him as a dependent, but I'm not sure if I can get his EIP because he didn't have a SSN in 2020.
Yes, you can receive a payment for your son (though he doesn't actually get anything himself.) For the first two Economic Impact Payments, an additional payment was made to taxpayers who had claimed a child who was 16 years old or younger at the time the payments were calculated. Since you didn't have your son listed on a previously filed tax return, nothing was advanced for you for a child dependent.
However, the recovery rebate credit can be claimed when you file your 2020 tax return. For that, you are entitled to a payment for each dependent child 16 or younger. When you tell TurboTax the amount that you actually received and it sees the dependent on the return (and not calculated in the payment amount) it will add this to your tax return as a credit on Line 30 of your tax return.
Sometime after you file your tax return and it is fully processed, you should also receive the $1400 payment.
The only wan you will not see an increase in your refund (or decrease in your balance due) for this additional payment is if you also have another child for whom you already received payment, who will not be on this return or who was17 or older in 2020. This is because the credit is calculated solely at the number of dependents, and not based on the specific individuals claimed.