The tax rates used for the excess were the marginal tax rates of the parents. Where I worked this year, many of these parents paid no taxes. They didn’t make enough money to do do; they got social security disability. So their marginal rates were zero or If they had some income, 10%. That’s a heckuva a lot less the 30-something rate of trusts and estates.
Also kids sometimes work which also uses up some of that $12k standard deduction.
It’s the low income kid that is hit hard with this change as you can see