The maker of M&Ms and Skittles has run rampant with its junk food advertising, quadrupling its number of breaches of a children's food marketing code in three years.

Food company Mars breached the "Responsible Children's Marketing Initiative" 102 times during a three-month period in 2014, up from 25 times two years earlier, the latest compliance report by the Australian Food and Grocery Council reveals.

While Mars reduced its violations from 2013, it was still by far the worst offender, accounting for a third of the total number of breaches in 2014 by the code's 17 signatories, which includes Coca-Cola and Kellogg's.

A screening of a junk food advertisement during a "children's program", defined as one with an audience comprising of at least one third children, constitutes one breach of the code.

Clare Hughes, nutrition program manager at Cancer Council NSW, slammed the self-regulatory code as "ineffective" as the total number of breaches had tripled in three years.

Campbell Arnott's, General Mills and PepsiCo are posting a higher number of offences each year.

"There's a lack of enforcement action and certainly no sanctions and penalties for breaching the code," Ms Hughes said.

"[Mars] is a repeat offender, advertising multiple unhealthy products to children, multiple times. If the penalty is just a rap over the knuckles, there's no incentive for it to change its marketing practices."

Ms Hughes said another problem was the code only covered advertisements aired during programs with an audience comprising of at least one third children.

The report said Mars' Skittles advertisement was "screened eight times in a children's program during the [three month] audit period, representing 0.1 per cent of all screenings of the advertisement".

This means the Skittles advertisement would have been seen by hundreds of thousands of children during general audience shows such as The Block and The X Factor hundreds of times over, based on children's viewing data by the Australian Communications and Media Authority.

In the report, Mars blamed two-thirds of its 102 breaches on the television networks' programming changes and bonus air time.

It did not respond to Fairfax Media's questions on the rest of the offences.

"Mars is ... concerned by the breaches ... [and] recognises there are still improvements to make and will partner with both internal and external stakeholders to enhance processes and ensure compliance," it said in the report.

PepsiCo, maker of Pepsi Max and Smiths Chips, breached the code 59 times in 2014, up from four times two years earlier.

Ferrero doubled its number of breaches with its advertisements for Tic Tacs, Ferrero Rocher and Kinder Surprise in that same period.

The RCMI code was introduced in 2009 in response to concerns the advertising of foods high in energy, fat, sugar and salt to children was contributing to Australia's obesity crisis.

A spokesperson for the AFCG, which administers the code, said the signatories were constantly working towards full compliance.

He said the overall compliance rate had slightly increased to 99.7 per cent.

"The RCMI initiative demonstrates world's best practice as complaints about advertisements are independently assessed by the Advertising Standards Bureau, and the compliance audit utilises data collected from an independent Australian advertising information service provider," he said.

Mars did not respond to requests for comment.