If the social security benefits were your only source of income for 2008, your benefits would generally not be taxable and you probably do not need to file a federal income tax return.
However, if you received income from other sources, your social security benefits will not be taxed unless your modified adjusted gross income is more than the base amount for your filing status. According to the IRS, a taxpayer may be able to determine whether or not their social security taxes are taxable by following the steps as outlined below:
Step 1. Add one–half of the total social security you received to all your other income, including any tax exempt interest and other exclusions from income.
Step 2. Compare this total to the base amount for your filing status. If the total is more than your base amount, some of your benefits may be taxable. The 2008 base amounts that are applicable to you as a joint filer are $32,000.
I suspect that none of the social security benefits received by the children would be taxable as well!