On the Form SSA-1099 for each dependent's Social Security benefits, the Beneficiary's Social Security Number in Box 2 at the top of the form should be the dependent's Social Security number.
You do not report your dependents' Social Security benefits on your own tax return. If either of your dependents files a tax return, the dependent has to include his or her Social Security benefits on his or her return. If the Social Security benefits are the dependent's only income, the dependent is not required to file a tax return and the dependent's Social Security income does not have to be reported anywhere.
