Harry, fourth in line to the British throne -- he'll move to fifth when brother Prince William's second child is born -- also shook hands and gave a high-five to ginger-haired 12-year-old Ethan Toscan, who brought a banner that read "Redheads RULE!"
Like in Britain, redheads are often teased in Australia, where they are known as "rangas" -- short for orangutans.
"He said that I was fabulous in making the sign and it's awesome to be a redhead," Ethan said later.
Young and old members of the public gathered at the memorial, as Harry laid a wreath at the Tomb of the Unknown Soldier before strolling to the museum's World War I and Afghanistan galleries.
Harry arrived at Sydney International Airport early Monday dressed in army fatigues, and changed into a dress uniform for the official functions at the memorial.
The 30-year-old veteran of two tours in Afghanistan later reported for duty to Air Chief Marshal Mark Binskin, Australia's defence Force chief, at the nearby Australian military officers' college.
Harry saluted his new boss, then delivered a letter from him his grandmother Queen Elizabeth II. She wrote that it was appropriate that her second grandson visited as the two countries commemorated sacrifices made a century ago during World War I.
Captain Harry Wales, as he is known in the British army, will be embedded with a number of Australian army units and regiments in the cities of Darwin, Sydney and Perth.
Nine Network reported that Harry made the 3,100-kilometer (1,900-mile) flight from Canberra to the northern city of Darwin in an Australian air force jet late Monday.
In Darwin, which will become a training hub for 1,050 US Marines in the coming weeks, Harry will work with a predominantly Aboriginal infantry regiment, the North-West Mobile Force, known as NORFORCE.
NORFORCE patrols vast tracts of Australia's sparsely populated northern tropical wilderness, covering 1.8 million square kilometers (695,000 square miles). It uses traditional indigenous skills, including tracking, in its surveillance work.
Harry, an Apache helicopter pilot, will be attached to an aviation squadron in the east coast city of Sydney and work with the elite Special Air Service Regiment, including Afghanistan veterans, in the west coast city of Perth. He will have to pass Australian certification testing before he is allowed to pilot any Australian aircraft.
He and his father, Prince Charles, will also attend centenary commemorations on April 25 in Turkey of the ill-fated invasion of Gallipoli peninsula during World War I in which Commonwealth forces under British command, including a joint Australian and New Zealand army, suffered heavy casualties.
-AP