Social Security benefits may be tax free or includible in gross income at 50% or 85%. This depends on a couple’s income, Social Security benefits, and tax-exempt interest. The fact that the benefits are payable to a third party does not change the tax result; the Social Security checks are being used for the taxpayer’s benefit.
The tax on the investment income in excess of $1,700 (may change after 2007) of a child under age 18, based on the parents’ marginal tax rate and computed on Form 8615.