You can claim your child as a dependent, regardless of age, as long as you meet all of the requirements. For example, you child can’t have gross income in 2017 of more than $4,050 and you must furnish more than half of his/her support. Note: For 2018 through 2025, there is no dependency exemption.
The tax on the investment income in excess of $1,700 (may change after 2007) of a child under age 18, based on the parents’ marginal tax rate and computed on Form 8615.