She says he has reduced his declared earnings from the business each year.

“He is obviously earning a lot more and doing cash jobs and hiding his income... With his child support decreasing by an extreme amount, I won’t be able to make ends meet. I know he is earning more than $100,000 annually.”

She says he was meant to pay just over $1100 a month between January and April but had only paid $473 in February.

From May his support will drop to $623 a month.

Her oldest son needs braces, which will cost $9000. Her middle child has an intellectual disability and toileting issues.

“I am on my feet constantly all day every day, I am up around six every morning and don’t get to bed until between midnight and 1am every day, I am unable to work as I also have a disability my legs are swollen and I’m still recovering from recent hernia surgery.

Child support liability is decided according to a person’s income, the amount of time they have the children in their care and their other children.

Overall, nine per cent of all self-employed taxpayers were declaring income of $30,000 to $40,000 a year, compared to 12 per cent of liable parents.

At the other end of the spectrum, 11 per cent of all self-employed were earning $100,000 to $150,000 but only eight per cent of those liable for child support.

Across all taxpayers, seven per cent of self-employed were earning $150,000 to $200,000 a year but only four per cent of liable taxpayers.

Across all self-employed people, 58 per cent were earning less than $70,000 compared to 70 per cent of those liable for child support and 72 per cent of all taxpayers, including those in all forms of employment.

Jessica Berentson-Shaw, from think tank The Workshop, says it's a recognised problem.

“It’s like a lot of these policies we need to update our systems to look at wealth - debt and assets. We know that income is simply not a sufficient measure of someone’s financial stability and ability to support their children and themselves.

“The world has changed and unearned income is increasingly a feature of well-off people’s lives. I also tend to think with children unconditional publicly funded child support still answers a lot of these problems including poverty.”

Robyn Walker, tax partner at Deloitte, says further investigation of the data is needed.

“You could definitely say there is evidence of lower incomes across the board with the liable parents cohort, when you’re looking at percentage of them,” she says.

“But is that actually evidence of any manipulation, or is it potentially more evidence that if you’re in a child support situation maybe you’re earning less because you’re potentially working less, juggling childcare responsibilities?”