Until recently, the kiddie tax only applied to children under the age of 14, but in 2005, the Tax Increase Protection and Reconciliation Act moved the age to 18, and the new legislation that was passed on Friday expanded it further: Effective Jan. 1, 2008, the kiddie tax will apply to children age 18 and younger as well as college students under the age of 24.
FORBES: The New Kiddie Tax