William and Kate joined by their children at carol service

The Prince and Princes of Wales’ children joined their parents at a carol service celebrating those supporting youngsters and families.

Prince George, Princess Charlotte and Prince Louis made a rare public for the annual Westminster Abbey event hosted by Kate which has quickly become a firm fixture in the festive royal calendar.

This year the service reflects the princess’ early years Shaping Us campaign launched in January, which aims to highlight and promote the significance of the formative years of a child’s life.

It was billed as a moment to thank all those who work to support babies, young children and families in communities across the UK and among the 1,500 guests were midwives and nursery teachers.

The royal children, George, 10, Charlotte, eight, and Louis, aged five, were introduced to the Dean of Westminster, Dr David Hoyle, outside the Abbey’s great west door when their first arrived with their father William.

Kate had travelled ahead of her family to meet and thank the celebrities taking part and she stopped to chat to a number of the young people invited to the event.

As they walked into the Abbey the royal children paused for a moment to post Christmas cards, in a special postbox, containing messages for children who might be struggling this Christmas, something open to all youngsters attending.

Among the highlights of the service will be songwriter and multi-instrumentalist Jacob Collier playing last Christmas on John Lennon’s piano, which was owned by Wham! singer and solo-star George Michael and loaned by his estate.

Broadcaster Roman Kemp, the son of Spandau Ballet bassist Martin Kemp and former Wham! backing singer Shirlie Kemp, will introduce Collier and talk about the role George Michael played in his life.

Oscar winning star Jim Broadbent will read an extract from Letters From Father Christmas by Lord of the Rings author JRR Tolkien and actor Michael Ward is due to recount the moment shepherds were told by an angel about the birth of Christ and they visited Mary and Joseph, in a reading from Luke’s Gospel.

Arriving guests were treated to carols and Christmas songs performed by the Action for Children Young Carers Aloud choir, made up of 12 young carers including one aged just six.

The princess thanked the celebrities for giving up their time when she met them ahead of the concert.

She appeared to joke with multi-instrumentalist Collier, who has posted music tutorial videos on YouTube, about her daughter learning the piano and he quipped “many a plink and a plonk”.

Chatting to Broadbent the princess said: “Thank you for your time because I know the lead up to Christmas can be busy for people.”

Kate walked around the Abbey before the concert started speaking to young people who have done inspiring activities.

She chatted to four scouts from the 3rd Upton Scout Group in Slough her family visited during the coronation celebration weekend, part of The Big Help Out event, helping to renovate their hut.

The princess told them “It was really inspiring-seriously good job” and high-fived each scout in turn.

Kate crouched down to chat to seven-year-old Oscar Burrow, from Lancaster, who when aged six climbed 12 mountains raising more than £40,000 for Derian House Children’s Hospice in Chorley, Lancashire.

His mother Kimberley Burrow said afterwards: “She said she’d heard about what he’s done and he’s doing a fantastic job, and hopes what he’s doing will inspire other children to do amazing things.”

The service began with the popular carol, Once In Royal David’s City, and the congregation also heard a duet by Beverley Knight and Adam Lambert who performed The Christmas Song, made famous by Nat King Cole.

William read the passage from the Gospel according to Luke that describes how Joseph and Mary travelled to Bethlehem to be registered and the birth of Jesus.

The Abbey echoed with the voices of its choir and the congregation singing a selection of carols including Silent Night, Holy Night and Joy To The World, as well as Hark! The Herald Angels Sing.

The historic building featured Christmas trees from Windsor Great Park donated by the King, which will be given to local communities after the service.

The event will be broadcast as part of Royal Carols: Together At Christmas, a special programme airing at 7.45pm on ITV1 and ITV X on Christmas Eve, featuring additional material including an introduction by Kate and films emphasising the importance of early childhood.

It will include contributions from Rio and Kate Ferdinand, Ugo Monye, Andrea and Virginia Bocelli and Dame Sheila Hancock.