Setting up an investment account for your children when they are very young is a great way to start saving for them but there may be unexpected tax consequences to consider. The Kiddie Tax applies to all children up to age 18 and students 19 to 23 who do not provide more than 50% of their own support. Under Kiddie Tax rules, a child’s investment income, such as dividends, interest, and capital gains in excess of $2,000 is taxed at the parents’ highest marginal rate.