Many <18 year-old workers don’t make enough to pay income tax, but this number is not zero. No one under 18 years-old is able to vote in this country, so the gov’t should not have the right to spend those tax dollars. This would also encourage young people to save up for a car, secondary education, or their own place to live after high school.
I couldn’t find data post-2010, but according to the Tax Foundation, workers <18 accounted for $13B of the U.S. AGI in 2010 … roughly 0% of the total. It’s a tax cut that would benefit young people and hardly affect the overall budget.
I would agree with the taxation without representation angle on this suggestion as long as the wages for someone <18 years of age doesn’t have that income counted towards their Social Security earnings when they are old enough to retire. We can’t have that benefit on both ends of the life cycle.