The two young royals will walk through the church in procession behind the late monarch's coffin as it is carried by the military bearer party.
WATCH: The Queen's grandchildren arrive for their vigil
Their grandfather, the King with the Queen Consort will process immediately behind the coffin, followed by Princess Anne and Vice Admiral Sir Tim Laurence, then the Duke of York, followed by the Earl and Countess of Wessex, and then William and Kate.
Prince Louis will not be present and is likely to be considered too young to attend.
While George and Charlotte will travel to Windsor for the committal service in St George's Chapel in Windsor afterwards, they will not be in the procession.
The three children, aged nine, seven and four, started their new school on the same day Her Majesty died at Balmoral on 8 September.
Prince George and Princess Charlotte will attend the Queen's funeral
When asked how her children were coping after losing their great-grandmother while appearing in front of crowds at Sandringham, Princess Kate revealed last week that "the children are doing well and they are being looked after at school."
However, one crowd member was told George was said to understand the loss of his great-grandmother more than his younger siblings. One well-wisher also explained: "She said they were keeping things as normal as possible for the children.
"She says the children were settling in well to their new school and Kate was grateful for the support. I joked I had to be quick because I had to do the school run and she said she was heading back to London to do it as well."
The children started a new school on September 8
The Queen's funeral will take place on Monday 19 September, following four days of Her Majesty's coffin lying in state at Westminster Hall.
The service will be conducted by David Hoyle, the Dean of Westminster, with Prime Minister Liz Truss and Patricia Scotland, the secretary-general of the Commonwealth, reading Lessons.
Prayers will be read by the current Archbishop of York, the Cardinal Archbishop of Westminster, the Moderator of the General Assembly of the Church of Scotland and the Free Churches Moderator.
At the end of the service, following The Last Post, two minutes' silence, the Reveille, and the national anthem, the Queen's Piper, Paul Burns, will play the traditional lament Sleep, Dearie, Sleep.
The coffin will then travel in procession from Westminster Abbey to Wellington Arch before moving to Windsor.
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