The kiddie tax rules have been changed to:

Pre-ARPA rules, allowing the childs unearned income to be automatically taxed at their capital gains tax rate.

Pre-TCJA rules, requiring that the childs unearned income is taxed at the parents marginal tax rate.

Pre-ARPA rules, giving the child the option of having their unearned income taxed at either their parents or their own marginal tax rate.

Pre-TCJA rules, allowing the child to automatically exclude up to $1,800 of unearned income.