Ads and signage for the memorial have used the words since the cultural institution adopted them as a centrepiece of its branding campaign in 2017.

The memorial has started removing the phrase, which was replaced in the national anthem on January 1 with "for we are one and free" to acknowledge Australia's Indigenous history.

A war memorial spokesperson said it would phase out printed advertising that used the old wording over the coming weeks and months.

It will remove the phrase "for we are young and free" from signage and electronic media as early as this week, the spokesperson said.

The wording has disappeared from signs outside the front of the memorial.

War memorial communications and marketing staff developed the brand campaign featuring the words more than three years ago. The memorial began using the phrase in its advertising after testing it with focus groups.

It has featured prominently in ads including at Canberra Airport and online, and on signage at the front of the war memorial.

The memorial's online shop sells can coolers and water bottles emblazoned with the words.

In its 2016-2017 annual report, the memorial said the use of the phrase in the branding campaign aimed to "encapsulate the memorial's unique goal of honouring Australia's servicemen and servicewomen whilst encouraging audiences to find a personal connection to their stories of service and sacrifice".

Then-war memorial director Brendan Nelson said in the report the branding acknowledged Australia was "a young country, and one that is free in large part due to the sacrifice of the men and women honoured here."

Dr Nelson in 2018 told a parliamentary inquiry into national institutions the word "young" referred to Australia's nationhood.

"Obviously, Aboriginal people have 60,000 years of history and custodianship here," he told MPs.

"But the paradox is that, too often, we take for granted these things that are most important to us.

"It is not really until you come to, in our case, the Australian War Memorial that you get a sense of why we are free - particularly, but not only, those one million Australian men and women who mobilised in the Second World War."

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Prime Minister Scott Morrison announced the change to the second line of the national anthem, Advance Australia Fair, on New Year's Day saying the new words would better reflect the nation's unity.

"Also, while Australia as a modern nation may be relatively young, our country's story is ancient, as are the stories of the many First Nations peoples whose stewardship we rightly acknowledge and respect," he said.

"In the spirit of unity, it is only right that we ensure our national anthem reflects this truth and shared appreciation."

The song had not changed since 1984, when it replaced "God Save the Queen" as Australia's national anthem.