The three children of the Duke and Duchess of Cambridge were dressed in a colour scheme of navy, white and blue for the first event of the four-day extravaganza.
Thousands of well-wishers got a glimpse of the young royals as they travelled in a carriage with their mother Kate and the Duchess of Cornwall.
Four-year-old Louis, who was wearing a sailor-style outfit reminiscent of one worn by his father in 1985, sat between his big brother and sister as they made their way to Trooping the Colour on Horse Guards Parade.
The trio waved at the crowds packed on to The Mall in central London.
At one point, seven-year-old Charlotte, wearing a summery cornflower blue dress with bow shoulder detail, could be seen pushing Louis’s arm down when he was mid-wave.
The oldest sibling, eight-year-old George, looked smart in a navy suit, white shirt and blue tie for the occasion.
During the Trooping ceremony, the children peered out of the window of the Duke of Wellington’s former office, and they could be seen pointing out towards the ceremony.
The children remained committed to waving at royal fans, and bowed their heads as they received a salute, on their way back to the palace in their carriage.
They then made an appearance on the balcony for the flypast which prompted some comical reactions from Louis who held his hands over his ears, probably due to the roar of the aircraft overhead.
Louis chatted with the Queen on the balcony, and once the flypast got going he could be seen covering his eyes, holding his head and resting his chin in his hands at various points.
The young prince was standing next to the 96-year-old monarch who smiled throughout as she looked towards the sky.