The income level cited by the expert is wrong.
If a child dependent earns more than $1250 in interest, they may be required to file a return and pay taxes.
https://www.irs.gov/individuals/check-if-you-need-to-file-a-tax-return
This is due to something called the "kiddie tax." Basically, Congress doesn't want parents to be able to avoid paying taxes at their higher rate by putting money in their kids' names. If the money is in a savings account or investment account, and earns interest, dividends or capital gains of more than $1250 per year, the child must file a return.
Note 1, that a child must always report income earned from working on a tax return in their own name, and if the child works and files a tax return, they must report all their interest, even if it is less than $1250.
Note 2, if the child does not work and their only income is interest and dividends, it is sometimes allowed to report that interest on a parent's return. But this is not allowed if the child also works (see Note 1).
