After you file

The child has a social security number now he was born in 2018 he's now 3 and I just barely have received is social security number a couple weeks ago it was never issued until a couple weeks ago I was not able to receive any stimulus or add him to any of my income tax these last 3 years he was just issued a couple weeks ago his social so my question is is there a way I can get back pay for the time that the pandemic started to now and I already started an amendment on my tax to add him as a dependent since I was not able to before