Kate and William dig deep in Canberra

Twins Oliver and Sebastian Lye helped Kate water in the newly-planted English oak tree. Photo / Getty Images

As a young girl pressed a Peter Rabbit soft toy into the hands of the Duchess of Cambridge in Canberra on Thursday morning, Kate gently asked "Is that for George?" and said "his cot's going to be full of little teddy bears".

Nine-month-old Prince George did not attend the royals' tree planting at the National Arboretum Canberra but his parents showed they were king and queen of the kids, lingering in the facility's playground and charming all on a stunning autumn morning.

Kate kneeled to talk to disabled children from the Black Mountain School and then watched on as 6-year-old twins Oliver and Sebastian Lye helped the royal couple water in the newly-planted English oak tree.

The boys were chosen because Sebastian has thrived despite difficulties from having Down syndrome and their mother Moira, who has battled cancer for years, has worked in the health sector and raised money for cancer support.

William praised the boys for doing a good job - "we'll done guys" - and said the tree would be "very healthy" after the thorough watering.

The event was among the more intimate on the tour with only 50 members of the public allowed in the arboretum, winning their place in a ballot in which there were more than 12,500 applications.

Kate, wearing a stunning emerald green Catherine Walker dress, particularly seemed to enjoy meeting the children, graciously accepting the gifts, asking their names and peppering them with lots of questions about the schools they attended.

"Oh, look at that. That's fun," she said of one toy for George.

"Super. Lovely peaceful spot," was William's summation of the arboretum.

Christine Wall, of Tuggeranong, said, "They're so impressive. It was so lovely to actually meet them. It's a once-in-a-lifetime opportunity."

Callan Bourke, 11, of Chapman, gave the royal couple copies of Diary of a Wombat by Jackie French and a touch and feel Steve Parish wombat book. His mother, Annie, said the royal couple said they would read the books to George tonight.

"They were so gorgeous, so beautiful. Very natural and lovely," Mrs Bourke said.

ACT Chief Minister Katy Gallagher said they chatted about the history of the site, a former pine plantation destroyed in 2001 fires and set aside as an arboretum in the wake of the devastating 2003 bushfires, with 100 forests planned for the hillside location.

The oak planted by the young royals was the 48th planting by a dignitary, with past high-profile planters including Danish Crown Princess Mary, the Sultan of Brunei and several visiting world leaders.

Kate and William later attended a reception at Parliament House and last night at Government House.

The royal couple will attend the national Anzac Day ceremony at the Australian War Memorial today.

- AAP