Child support is not considered taxable income for the recipient. Because of this, it is not included in calculating a person's gross income for a tax year. In addition, it is not eligible for a deduction by the individual who pays the child support.
Child support is also ineligible as income in regards to calculating income to qualify for the Earned Income Tax Credit. There is actually not a form that taxpayers use to include child support payments, so it is not factored into a filing at all. However, claiming the child as a dependent is an option for either parent, depending on their arrangement.