I just realized that I accidentally claimed my son on my taxes and because of this mistake he cannot get the stimulus check?

[Critter]

Well  you can amend your return now (and give up the $500 you got for him on the return)  and he can file (or amend) his return  to qualify for the stimulus (if the IRS will allow it )  OR   he can wait and  get the credit on the 2020 return he will file next January.