I agree if you are calculating support for determining dependency. It is evident in the support test worksheet that the money must be spent.
But still - the corresponding test for Kiddie Tax is only as described in the instructions for 8615 . There it lists the criteria below for who must file. Part 3c does not make any reference (nor can I find any other reference) that the earned income must be spent. Only that you have to have it.
Form 8615 must be filed for any child who meets all of the following conditions.
The child had more than $2,200 of unearned income.
The child is required to file a tax return.
The child either:
Was under age 18 at the end of 2021,
Was age 18 at the end of 2021 and didn’t have earned income that was more than half of the child's support, or
Was a full-time student at least age 19 and under age 24 at the end of 2021 and didn’t have earned income that was more than half of the child's support.
(Earned income is defined later. Support is defined below.)
At least one of the child's parents was alive at the end of 2021.
The child doesn’t file a joint return for 2021.
