Final answer:
The kiddie tax ceases to apply when a child turns 19 unless they are full-time students and under 24 years old. Conditions include the child's earned income not exceeding half of their support costs for the year.
Step-by-step explanation:
The notion that a child reaching the age of 19 is no longer subject to the kiddie tax is based on U.S. tax law. The kiddie tax is a tax on the unearned income of children under certain conditions and ages. The goal of the tax is to prevent parents from avoiding taxes by shifting large amounts of investment income to their children, who typically are taxed at a lower rate.
As per the IRS rules, the kiddie tax does not apply to individuals who are aged 19 or older unless they are full-time students and under the age of 24 at the end of the year, and their earned income does not exceed half of their support for the year. Once a child turns 19, and if they're not a full-time student, or they turn 24 if they are a full-time student, the kiddie tax no longer applies.