Thousands of Kiwi parents owe more than one-billion-dollars in child support - with some debts dating back more than 30 years

More than $400-million of that is in penalty fees.

Included in the list of unpaid child support owed is a 10-year-old debt of $2.5-million.

Inland Revenue won't say how it came to be that size but says it's currently under a payment arrangement.

It says there are different collection methods it can use, including legal action -- but says some parents actively avoid paying.