The AMT originally came into being as a way to make sure wealthy taxpayers don’t use too many legal deductions to drive down their tax bill to unreasonable levels. However, with time, more and more middle-class people have become affected by it.
In order to prevent Mom and Dad from shifting their investment income to their children to hide gains, Congress created “kiddie tax” rules. This makes any income earned by children taxable at a higher tax rate than they otherwise would as a non-dependent.