Do you have more than $350 in investment income, or other unearned income such as unemployment compensation? You may be subject to the "kiddie tax". This is designed to prevent parents from putting investments in their children's names to avoid tax by using their child's standard deduction and lower tax rates to pay less tax on those investments. The income tax you pay on unearned income is calculated based on your parent's income. The kiddie tax applies to all unearned income including investments, dividends and unemployment compensation.
https://www.irs.gov/taxtopics/tc553
https://www.irs.gov/pub/irs-pdf/p501.pdf
