Kate could be seen guiding her eldest son, nine, and daughter, seven, into the world-famous abbey.
Prince George and Princess Charlotte travelled to Westminster Abbey in the same car as Queen Consort Camilla, with Kate arriving with them.
She held her daughter's hand as George led the way, with Charlotte appearing inquisitive as she took the scenes in.
They arrived at the church shortly after some of the Queen’s grandchildren, including Princess Beatrice and Princess Eugenie.
The future king could be seen looking nervous, with his mother and sister behind him.
Kate, George and Charlotte arriving at Westminster Abbey
JOHN SIBLEY
Kate with George and Charlotte
PHIL NOBLE
It came as Prince William put aside his differences with Prince Harry to walk side by side in an emotional show of unity behind Queen Elizabeth II's coffin.
With thousands of mourners in London to pay their respects to the late monarch, the Prince of Wales and the Duke of Sussex followed King Charles III in the walk towards Westminster Abbey.
They were joined by the wider Royal Family – with the King, Princess Anne, Prince Andrew and Prince Edward taking leading roles.
The royals will join dignitaries from around the world in the more than 1,000-year-old abbey as they pay their respects to the beloved Queen Elizabeth II.
After proceedings conclude, the procession will set off for Wellington Arch at Hyde Park Corner. The state hearse will later depart on its journey to Windsor as the parade gives a royal salute and the National Anthem is played.
Kate and William will depart for Windsor by car, following the King – joined by Queen Consort Camilla.
A committal service will take place in Windsor Castle's historic St George's Chapel this afternoon, after which members of the Royal Family will depart the Galilee Porch and bring a close to the public ceremonial arrangements.
A private burial service will be conducted by the Dean of Windsor at 7.30pm, attended by the King and members of the Royal Family.
Queen Elizabeth II will then be buried together with her beloved Prince Philip, Duke of Edinburgh, at the King George VI Memorial Chapel.
