The Tax Cuts and Jobs Act is the biggest federal tax law change in over 30 years. Below are some significant changes affecting individuals. Note: Except where noted, the changes are effective for tax years 2018– 2025. Kiddie Tax. Generally, the Kiddie Tax applies to certain children with unearned (investment) income that exceeds $2,100. For tax years 2018 through 2025, the tax is computed by applying the tax rates applicable to estates and trusts to the net unearned income of