How do I get my son's first two stimulus that he didn't get what form is it when I claim him in 2020 taxes

Did you file a 2020 tax return?   Did you claim your son as a dependent?   If you filed a 2020 return and claimed your son, then the recovery rebate credit for the 1st and 2nd stimulus should have been on line 30 of your Form 1040.   The amount for the 1st stimulus for claiming a child under the age of 17 was $500; the 2nd stimulus amount for claiming a child under 17 was $600.   So is there $1100 on line 30?

If you filed but did not claim your child you can file or amend your 2020 return to use the recovery rebate credit to get the 1st and/or 2nd stimulus.  The credit is found in the Federal Review section.

@Anciearias2  - if he was your dependent and eligible for the stimulus, it would ahve been on your 2020 tax return 

What is on Line 30 of Form 1040 from 2020? 

how old is your son?  If he was older than 16 in 2020,  you were not eligible to claim either of the 1st two stimulus for him.  Only for the 3rd stimulus (2021) were you able to claim your dependent over the age of 16 for the Recovery Credit / stimulus.