A child can get a tax file number (TFN) at any age (there is no minimum age).
Children are not exempt from quoting a TFN.
Interest
If a child quotes their date of birth, they are entitled to a threshold of $420 per income year on interest. If they don’t quote their date of birth, the threshold is the same as the adult threshold of $120 per income year.
Where the total interest earned during an income year is $420 or more
if the child quotes a TFN,the investment body will not withhold pay as you go (PAYG) tax, and
if the child does not quote a TFN, the investment body will withhold PAYG tax at 46.5%.
This applies to the total interest earned (not just the amount above $420, or the payment period threshold equivalent).
If the child has had PAYG tax deducted, they will need to lodge a return to claim these amounts back from the Tax Office. A child who does not have a TFN will need to get one before they can lodge a return.