If the 1099-INT has the child's Social Security number, the interest is the child's income, not your income. It should be reported on the child's tax return, not your tax return, regardless of the child's age.
In some cases it is possible to report a child's income on the parent's tax return. The only advantage of doing that is that it's less paperwork. It will not save any tax, and in many cases you could end up paying more tax overall than if you filed separate returns for the children. You are never required to report a child's income on your tax return, regardless of the child's age.
If a dependent child's total investment income, including the interest, is $1,250 or less, and the child has no other income, the child is not required to file a tax return. In that case, the child's interest income does not get reported anywhere.
If a child's unearned income is $2,500 or less, that child does not pay kiddie tax. Unearned income is basically any income that is not from working.
The $1,250 and $2,500 figures are for 2023. For 2024 the amounts are $1,300 and $2,600. They are adjusted for inflation each year.
