Prince George, Princess Charlotte, Prince Louis and cousin Mia Tindall joined William and Kate to greet well-wishers before the morning service at St Mary Magdalene Church in Sandringham, Norfolk.
The young royals looked confident as they mingled with the public outside the ceremony, with George and Charlotte seen having friendly chats with members of the public.
Louis, 5, was seen being escorted around the property by Prince William, who also helped young Mia Tindall – the daughter of Zara Phillips and Mike Tindall.
The traditional royal celebrations are once again taking place at the private Norfolk estate, with most of the family in attendance – with the exception of the Duke and Duchess of Sussex, who are spending the day in LA with their children, Prince Louis and Princess Lilibet.
The King and Queen, along with the Princess Royal and her husband, Vice Admiral Sir Timothy Laurence, waved to well-wishers as they attended a Christmas Eve service at the church on Sunday.
Royal Christmas traditionally involves welcoming people outside the church and having a family dinner with turkey and all the trimmings.
The Prince and Princess of Wales go to church with their children, Princess Charlotte and Prince George, who holds the hand of Mia Tindall
Prince Louis grinned as he shared a joke with Mia Tindall on Christmas morning
George, Mia and Charlotte were seen exchanging a joke at the corner of the meet and greet
Prince William was on hand to help Louis greet well-wishers who had waited hours for a glimpse of the royal family
Prince George smiled as he greeted the public outside the church
Prince George appeared adept at the role as he was guided in his duties by Kate
Louis and Mia Tindall demonstrated their close bond as they made their way through the event
The Princess of Wales put her arm around Prince Louis for comfort as they arrived at church on Monday
The King and Queen will celebrate Christmas Day with other members of the Royal Family at Sandringham
Sandringham House was the private home of four generations of British monarchs for more than 160 years and is now owned by the King.
King Charles was seen waving to the crowds who had gathered outside Norfolk church to wish him and his family a happy Christmas as he walked alongside Queen Camilla.
The Princess of Wales smiled broadly as she walked to church in an elegant blue coat and matching hat, holding the hand of her daughter Princess Charlotte.
Her younger brother Prince Louis joined the rest of his family and held the hand of his second cousin Mia Tindall as they prepared for the service.
He grinned cheekily at the crowd and told a joke with nine-year-old Mia, who was wearing a long purple coat.
Their appearance side by side, followed by the rest of their family, suggests a budding friendship between the two.
Zara and Mike Tindall held the hands of their other daughter Lena while their youngest child Lucas, two, stayed at home.
The mother of three wore a long green coat with a custom gold headband by Juliette Botterill.
On his other side, Prince William also held his son's hand, while Prince George walked alongside his sister in a navy blue suit.
Princess Eugenie and husband Jack Brooksbank leave after the Christmas service
Kate was seen driving Louis as they left the church this morning
King Charles waved to the crowd as he and Queen Camilla walked to the small chapel
Prince Louis of Wales and Mia Tindall attend the Christmas morning service at Sandringham Church on December 25
The Princess of Wales held her daughter Princess Charlotte's hand on the way to the service
Queen Camilla welcomed around 1,000 well-wishers in front of the church today
Kate and Charlotte smile at the crowd gathered to see the royal family at Christmas
The Duke and Duchess of Edinburgh were at church this morning with the rest of their family
The Princess Royal arrives at the church for the church service in Sandringham this morning
Lady Louise Windsor accompanies her parents, the Duke and Duchess of Edinburgh, to church
Prince Andrew's ex-wife Sarah Ferguson also joined the rest of the royal family on Monday
Jack Brooksbank and Princess Eugenie at the Christmas morning service at St Mary Magdalene Church in Sandringham, Norfolk
Zara Tindall, Lena Tindall and Mike Tindall followed their Mia, who walked alongside Prince Louis
Kate, dressed all in blue, with Princess Charlotte, who wore a long green coat
The Princess of Wales briefly put her arm around Prince Louis' shoulders for comfort before entering the church.
They walked behind the king and queen, who were greeted by about a thousand local residents, many of whom had waited for hours on Christmas morning to catch a glimpse of the family.
For the second year in a row, the disgraced Duke of York attended church with the Sandringham family.
Andrew's alleged links to convicted sex offender Jeffrey Epstein will face further scrutiny in the new year with the release of hundreds of files from a libel case following a ruling by a US judge.
His ex-wife Sarah, Duchess of York, made her first public appearance at Sandringham in years, walking alongside her ex-husband and smiling broadly at the press.
Andrew's daughters were with their husbands, Princess Beatrice with Edoardo Mapelli Mozzi and Prince Eugenie with Jack Brooksbank.
The Duke and Duchess of Edinburgh joined the rest of the royal family on their way to church. The Duchess of Edinburgh wore a tailored version of the Claire Mischevani Kristen coat.
After the service, the royal family spoke to the public who had gathered outside the church.
The Duchess of Edinburgh smiles as she passes crowds of people on her way to church
Prince Andrew (left) joined his family along with his ex-wife Sarah Ferguson and their daughters Princess Beatrice and Princess Eugenie
Lena Tindall went between her parents Mike and Zara Tindall
Lady Margarita Armstrong-Jones and the Earl of Snowdon at the Christmas morning service
Members of the Royal Family attend a Christmas service at Sandringham alongside the King and Queen
Charles' second Christmas message as monarch will be broadcast at 3pm and this year it was recorded in the Center Room at Buckingham Palace, which leads to the royal residence's iconic balcony.
The room is decorated with a live Christmas tree, which will be replanted after the broadcast.
Natural and sustainable decorations hang from its branches, including hand-turned wood, dried oranges, glass balls, pine cones and paper.
Charles, like Queen Elizabeth II, writes his Christmas broadcasts and last year he followed his mother's tried-and-tested template, a personal reflection of the year that touches on contemporary issues and has a Christian framework.
The king will deliver his second annual royal speech, with a focus on the environment.
It marks a departure from the typically apolitical speeches of his mother, the late Queen Elizabeth.
The King appears to be recycling his speech suit – he was pictured in the same blue single-breasted suit he wore to the Christmas message last year.
He has previously stressed the importance of re-wearing clothes, saying: “People throw away so much when they could easily repair it.”
A BBC documentary about the King's first year on the throne, to be broadcast on Boxing Day and produced by the Mail's Robert Hardman, shows behind-the-scenes footage of last year's Christmas broadcast, which was watched by 10.6 million viewers in the UK.
The film opens at Windsor Castle on December 13, 2022 and shows the King saying the message: “Well, I've really done it all.” This speech was recorded in St George's Chapel and included a moving tribute to his deceased mother who is buried there.