How do I file for all the checks that came w each stimulus for my son?

You enter the amounts you actually got including any for your dependent.  You enter the total you got for each round #1 and #2.  You don't enter the 3rd round on your 2020 return.

When you go through the federal review tab it will ask how much you got if any.  Enter a 0 in the box if you didn't get one.  Or to enter your stimulus payment in TurboTax, type "stimulus" (without the quotes) in the Search box, then click the link that says "Jump to stimulus."

After you have entered your tax information and are ready for the Federal Review, it will be the first question.

If you are trying to trigger it, you can go to Other Situations, answer any questions and click Done. The next automatic selection is Federal Review and it will ask about payments received.

If you didn't get one or both of the Stimulus payments or qualify for more it will be the Recovery rebate credit on 1040 line 30.  It either adds to your refund or reduces a tax due.