Should my tax return be rejected if my girlfriend agrees to let me claim my son?

[Carl]

No. But if your GF claimed him (assuming she is the mother of your child) and her tax return has already been accepted by the IRS, then you can't claim him.

[IreneS · Accepted solution]

Even if your girlfriend let you claim your son as a dependent, she can claim the child on her return for the purposes of the earned income credit and child care credit.

If the child's SSN appears on her return (even though she is not claiming him as a dependent)  and she filed before you you will not be able to e-file.  Just print your return and mail it in.