Prince George and Princess Charlotte were the stars of the show on a packed Buckingham Palace balcony, as they watched open-mouthed at an RAF flypast for Trooping the Colour.
The young Royals joined the Queen, Duke of Edinburgh and the wider Royal family for an annual appearance, waving to large crowds outside the palace.
The Prince, whose father the Duke of Cambridge is an air rescue pilot, had appeared initially underwhelmed by his public duties, resting his chin in his hands as his family assembled in front of the cameras.
But as the flypast began, he appeared transfixed, bouncing on his toes as he waited for the next plane to arrive.
His sister Princess Charlotte, wearing pink to match her mother, was entertained in the Duchess of Cambridge's arms before being carefully supervised standing next to Prince George on a box on the balcony, to be clearly seen by crowds.
Isla and Savannah, the daughters of Peter and Autumn Phillips, charmed the crowds as they appeared to match RAF planes overhead to a picture book in their hands.
As the Duke and Duchess of Cambridge kept a close eye on their children, the Queen and Duke of Edinburgh took centre stage at Buckingham Palace as they observed the crowds of well-wishers.
Earlier in the day, the Queen had issued a message to the nation, acknowledging sorrow over the "terrible tragedies" in London and Manchester over the last few weeks.
They held a minute's silence to honour all those affected.
The Queen celebrated her official birthday today as she was joined by her family for the annual display of pomp and pageantry.
The event saw more than 1,000 soldiers taking part, and went ahead after the Queen spoke of her pride in a nation rallying after "terrible tragedies" in London and Manchester.
The Duchess of Cambridge wore a pink dress by Alexander McQueen and hat by Jane Taylor, and the Duchess of Cornwall an Anna Valentine cream chiffon dress and coat with a Phillip Treacy hat.
With the Duke's recent announcement that he will retire from public duties after the summer, this may have been the last time the public see him play such a visible role in the ceremony.
The Duke of Edinburgh chose this year to wear morning dress instead of full uniform, and sported a Household Division tie, Garter Star and Medals.
The Queen wore a Stewart Parvin outfit – a pale blue jacquard silk duster coat with matching shift dress – and a hat by the late Philip Somerville with the large Guards brooch.
The Prince of Wales rode horse George and wore the Guard of Honour uniform. The Duke of Cambridge wore his Irish Guard's Tunic with Jubilee medals, sword and bearskin, and rode Wellesley.
The Princess Royal, on Sir John, wore her Colonel of the Blues and Royals uniform, with medals.
The procession was accompanied by a Sovereign's Escort of the Household Cavalry, made up of Life Guards and Blues and Royals, in their silver and gold breastplates and plumed helmets.
The Colour paraded on Horse Guards this year was the flag of the 1st Battalion Irish Guards.
Four of the five Foot Guards regiments of the Household Division – the Grenadier, Coldstream, Scots and Irish Guards – marched in the parade wearing bearskin hats and red tunics.
The Household Division Bands and Corps of Drums also took part, as will the King's Troop Royal Horse Artillery who, following the parade, fired a 41-gun salute in Green Park to mark the Queen's official birthday.
Trooping the Colour originated from traditional preparations for battle. Colours, or flags, were carried, or ''trooped'', down the rank so that they could be seen and recognised by the soldiers.
In the 18th century, guards from the royal palaces assembled daily on Horse Guards to ''troop the colours'' and in 1748 it was announced that the parade would also mark the Sovereign's official birthday.
The Queen's actual birthday was on April 21, when she turned 91.