Spare son dicey details of who's a father
If at all possible, you, your ex and your current husband should meet in the office of a family counselor to talk this through. The truth should be disclosed. Your son is at an extremely tender age. Your counselor might suggest that you wait a few months. Your ex may choose to formally and legally adopt him.
You should also abandon any mention of child support. If you had wanted to make a child support claim, you should have handled it many years ago.
It would be a mistake to imply to your son that there is any sort of financial issue on the table.
LIers missing in Nepal disaster ... Countdown to Hofstra strike ... 175-mile 'Greenway' plan ... Chicken finger hot spot