Greg Mankiw has a terrific post that sums up how the tax proposals of McCain and Obama would affect his incentive to work more on the margin.
If there were no taxes, then $1 earned today would yield my kids $28. That is simply the miracle of compounding.
Under the McCain plan, a dollar earned today yields my kids $4.81. That is, even under the low-tax McCain plan, my incentive to work is cut by 83 percent compared to the situation without taxes.
Under the Obama plan, a dollar earned today yields my kids $1.85. That is, Obama's proposed tax hikes reduce my incentive to work by 62 percent compared to the McCain plan and by 93 percent compared to the no-tax scenario.