Benefits such as monthly retirement, disability and survivor may all be taxed as income. However, supplemental security income (SSI) isn't taxable.
The base amount is set by the IRS and can be found in Publication 915. Currently, the base amount is $25,000 if you're single and $32,000 if you're married and filing jointly. The base amount drops to zero if you're married filing separately, unless you lived apart for the entire year.
Survivor benefits can be taxable income just like retirement benefits and are calculated the same way. You would use the total income of the person who has the legal right to the survivor benefits for the calculation. If only your child has a legal right to the benefits, only his income is used in the calculation.