Exclusive: Prince George, Princess Charlotte and Prince Louis join Will and Kate at scouts hall for King's Big Help Out

LONDON – – Prince George, Princess Charlotte and Prince Louis made a surprise – and very rare – appearance on a working engagement with their parents to celebrate the King's coronation.

The three Wales children joined Prince William and Catherine, Princess of Wales at the 3rd Upton Scouts Hut in Slough, just outside of London, on Monday to help repair the ageing building and its grounds.

But they were also there to have fun, the occasion marking five-year-old Louis' first official engagement.

Watch the video above.

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And 9Honey was lucky to be there as the family arrived for the community-minded day, aimed at leaving a legacy from the historic coronation.

Princess Charlotte, eight, and Prince Louis each took turns at archery and impressed the gathered scouts, with their arrows consistently hitting the target.

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Before the fun and games though, they got stuck with with a bit of hard work.

Prince George, nine, helped his father drill holes into a wooden box, capably holding the tool while still under the watchful eye of the adults.

Princess Charlotte enthusiastically re-varnished part of the wooden door while little Prince Louis took control of the wheelbarrow.

He was seen expertly shovelling in dirt from a bag into the wheelbarrow before wheeling it away – and he looked like he was enjoying every minute of his first ever royal engagement.

Louis was also seen getting inside a digger, sitting on Prince William's lap, before helping to move dirt.

But when it came to toasting marshmallows by a camp fire, Louis got smoke in his eyes.

The children also helped volunteers reset a path, dig a new soakaway, add planters to the front of the building and paint a mural.

While he has joined his parents on other, big royal occasions, Monday's was Louis' first working event.

The Wales' outing was part of The Big Help Out, a national day of volunteering to mark the end of the three-day coronation weekend.

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Their visit was kept tightly under wraps with only a very small group of media present. At first it was only thought Prince William and Kate would be there.

The inclusion of George, Charlotte and Louis was kept secret until the very last moment.

The family spent close to an hour at the scouts hall and as they left, the Princess of Wales said a special hello to 9Honey.

The royal mum then told a member of the public that Princess Charlotte is in year three at school before she and the children got into their waiting car.

Kate, who is joint President of the Scouts Association, seemed amused as she waited for Prince William to join them as he was taking photos with the club's members.

He soon caught up and got behind the driver's seat; whisking the family away.

The event has capped off a very busy weekend for the Prince and Princess of Wales and their children who took starring roles in the King's coronation on Saturday and the older siblings who enjoyed the concert on Sunday.