The King, Princess Anne and Prince Edward wore ceremonial uniform to accompany the slow procession of the Queen's coffin through Edinburgh.
Prince Andrew, who also walked behind the cortege, wore service medals on morning dress because he is not a working Royal.
The Queen's children accompanied her hearse on foot from Palace of Holyroodhouse up the Royal Mile to St Giles' Cathedral.
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Charles III was wearing the rank of Field Marshal and 10 medals, including a Queen's Service Order medal, Coronation medal, Silver, Golden, Diamond and Platinum medals, Naval Long Service Good Conduct medal, New Zealand Commemorative medal, New Zealand Armed Forces Awards and a Canadian Forces Decoration.
Princess Anne, who holds the ranks of Admiral in the Navy, General in the Army and Air Chief Marshal in the RAF wore 11 medals, including Order of St John Service Medal and a New Zealand 1990 medal, and three decorations – the Most Notable Order of the Garter, the Most Ancient and Most Noble Order of the Thistle and the Royal Victorian Order.
The Duke of York wore 10 medals and the Earl of Wessex had six.
The Duke, a former Navy pilot who served in the Falklands War, is expected to don uniform once in the 10 days of mourning, on Sunday for the vigil around the Queen's coffin during the lying in state in Westminster Hall.
Her Majesty will lie in St Giles' overnight before the coffin is flown to London on Tuesday.
Crowds lined the streets as the King led the Royal Family in a poignant procession behind the coffin of his mother, through the Scottish capital, with an escort provided by the Royal Regiment of Scotland and the King’s Body Guard for Scotland (the Royal Company of Archers) and a pipe band with drums muffled.
A bearer party from the Royal Regiment of Scotland carried Her Majesty's coffin into St Giles' Cathedral following the procession from the Palace of Holyroodhouse, where her family, and a congregation drawn from all areas of Scottish society, attended a service of thanksgiving to celebrate and reflect on her life.
King Charles III and the Queen Consort arrived in Edinburgh earlier on Monday.
They were greeted at the Palace of Holyroodhouse, the official residence of the Sovereign in Scotland – where the Queen's coffin had been lying at rest in the throne room – and the King carried out an inspection of a guard of honour from The Royal Regiment of Scotland.
A Royal Salute of 21 rounds was fired from Edinburgh Castle by 105th Regiment Royal Artillery as the King arrived at the palace.
Watch: First Changing of the Guard of King Charles' reign takes place.
King Charles also took part in the ancient Ceremony of the Keys at the Palace, where he was handed the keys to the city by the Lord Provost.
In keeping with tradition, he handed them back, entrusting their safekeeping to the city's elected officials.
The Ceremony of the Keys is a tradition that takes place each year at the palace in Edinburgh, and would once have taken place at the start of the Queen's summer holiday in Scotland. She last took part in the ceremony in July 2022.
On arrival, the monarch is presented with the keys of the city of Edinburgh by Lord Provost before, according to tradition, they are then handed back, into the trust of the city with Edinburgh's elected officials.
King Charles spent time meeting members of the public and shaking their hands, receiving flowers, before joining other members of the Royal Family for the procession along the Royal Mile to St Giles' Cathedral.