Kate's 'mum moment' at Trooping the Colour: Gently corrects Prince Louis's bad habit

The Duchess of Cambridge has been caught in a classic 'mum moment' during the Trooping the Colour event on Saturday.

It was while the royals were assembled on the balcony of Buckingham Palace to observe the colourful RAF flyover that Prince Louis, one, was spotted sucking this thumb.

When mum Kate noticed her toddler indulging in the bad habit, she gently removed his thumb from his mouth.

The tired prince didn't seem happy to be corrected.

Early in the day when the Cambridge children were seen waving from one of the windows of Buckingham Palace, the young prince was photographed with his thumb firmly in his mouth.

Older siblings Prince George, five, and Princess Charlotte, four, have never been spotted sucking their thumbs.

Not all children develop the bad habit, with most parents choosing the same path as the Duchess of Cambridge, gently correcting the habit until their children grow out of it.

Featuring almost 2000 soldiers and musicians, the Trooping the Colour parade is held annually in June to mark the official birthday of the British sovereign.

It entails a procession from Buckingham Palace to the Horse Guard's Parade, concluding with an Royal Air Force flypast, which the royals enjoy from the balcony.

The Cambridge children seemed to enjoy this year's event, with photos of the adorable trio delighting royal fans.