If all of your are living together as a family----and that is what it sounds like in your post -----the child's Social Security number can only be used on ONE of your tax returns---not on both. If you already claimed the child, then the child's father should just file Single and not enter anything about the child on his own tax return. Using the child's SSN will cause his e-file to be rejected. It has already gone into the system when you used it.
The IRS does not need to "see" that he has a son. The IRS knows that children can have two parents. Sometimes divorced or never married parents who do not live together have a signed agreement and there is a "custodial" parent and a "non-custodial" parent who share the child credits. That does not sound like your situation, so you would not both enter information about the child or an "agreement."
If that is incorrect, and you and the other parent do live apart, then post back for further help.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
