The first $1,100 of net unearned income of a child ( someone under age 19, or under age 24 if a full-time student) is tax free.
The next $1,100 is taxed at the child’s rate. Any unearned income above $2,200 is taxed at the ordinary income and capital gains rates that apply for trusts.
Earned income of children is taxed at the individual tax rates for single filers.