You say "According to my original divorce decree, this is my husband's year to claim our son his taxes".
That infers that you claimed the child, on your 2019 return, and got the $1100 (500 + 600) child stimulus money (assuming the child is under 17).
You might be interested to know that due to loop hole, in the covid law, your ex will be allowed to claim the same $1100 on his 2020 tax return, if he claims the child as a dependent.
