Income less than $18000 for dependent child - capital gains

[MomtoJS]

My dependent child has capital gains of $12,000 on 1099B - why is he being taxed?

[AlexisH]

Hi there-  you have a couple of factors going on here. Since your dependent child is claimed as a dependent the standard deduction amount is reduced for dependents. 

For 2019, the standard deduction amount for an individual who may be claimed as a dependent by another taxpayer cannot exceed the greater of $1,100 or the sum of $350 and the individual’s earned income (not to exceed the regular standard deduction amount).

There are also change in tax rates. The Tax Cuts and Jobs Act of 2017 has modified the tax rates and brackets that you will use to figure the tax on your 2018 unearned income. Your tax rate is no longer affected by the tax situation of your parents or the unearned income of any siblings. Instead, all net unearned income over a threshold amount of $2,100 for 2018 is taxed using the brackets and rates for estates and trusts. 

There is a chart on page one here that shows the rates https://www.irs.gov/pub/irs-pdf/i8615.pdf