After you file

How did you 'accidently' claim your son last year?

 

If you CAN claim him, you don't have to. 

 

but from your son's perspective, if someone CAN claim him, even if they don't, he has to answer that way.  (and if someone CAN claim him, even if they don't, he is not eligible for the stimulus.... if that is why you are really asking)