Wooden crosses inscribed with the personal reflections of Australian school children will be placed on 15,000 overseas war graves this Anzac Day.

It is part of a project by the Australian War Memorial (AWM) which will see 100,000 crosses sent overseas during the next four years, marking the centenary of World War I.

AWM director Brendan Nelson says the crosses draw on the children's feelings after visiting the memorial.

Sorry, this video has expired Students send messages of thanks to fallen soldiers ( Narda Gilmore )

"From the students who've completed the crosses, the constant theme is 'thank you for your sacrifice, thank you for giving your life for us and thank you for helping us to be free'," he said.

Dr Nelson says thousands of crosses have already been sent overseas.

"For Anzac Day this year, in 16 countries these crosses will be placed by Australian children who've written their message of what it means to them," he said.

"It's not only what Anzac Day means to them, but more importantly what the sacrifices of these men and women means to them 100 years on."

Eliza Niven from Lyneham High School says she spent a long time deciding exactly what to write on her cross.

"It's definitely a privilege to do this so that I can speak about what it means to me," she said.

"I ended up writing 'your bravery gave us peace'."

Emma McMaster from Ainslie Primary School says it is an honour to help commemorate the centenary of WWI.

"It's very exciting because you get to write something to soldiers who have fought for our freedom in the past," she said.

Fourteen crosses and their messages will adorn wreaths for Anzac commemorations in Canberra, with two of them to be laid by the Duke and Duchess of Cambridge.