A little boy was so overwhelmed when meeting the Queen that he dropped to his knees and crawled out of the nearest door.
Nine-year-old Nathan Grant was so starstruck upon being introduced to the monarch by his adoptive parents, former Fame Academy judges David and Carrie Grant, that he bolted out of the room, shouting "bye" as he left.
Onlookers can be seen laughing in a video captured during the exchange while the Queen visited Coram, the UK's oldest children's charity.
Based at the site of The Foundling Hospital in London, Coram has been helping vulnerable children since it gained the Royal Charter in 1739.
The Queen visited the charity to open The Queen Elizabeth II Centre — a national centre for children named in her honour.
The centre has been launched as a celebration of the 350th anniversary of the birth of the founder, Thomas Coram.
The Queen was dressed in a jade green coat by Stewart Parvin and matching Rachel Trevor-Morgan hat, with a dress in floral silk in the shades of jade, mint, lavender and magenta. A diamond lily brooch finished the outfit.
Her Majesty was greeted on arrival by Edward Newton, 102, the oldest surviving pupil from The Foundling Hospital.
Mr Newton mentioned to the Queen that he remembered King George's visit to the hospital in 1926, saying "I was a little tot".
Author Dame Jacqueline Wilson was also among those who attended.
Dame Jacqueline, who was one of the first Coram fellows, said: "I just think it's a wonderful organisation and it's very much to do with helping children now in new ways.
"I thought it was a lovely occasion. There was a sort of mixture of formality and informality which worked really well - and the Queen was smiling!"
During the tour the Queen met eight-year-old Lewis, who asked her which was her favourite of the countries she had visited.
She replied that it was a difficult question, saying there are "so many I couldn't pick one".
The day was particularly special for Lewis as it marked one year since he moved in with his adoptive family.
Later the Queen went outside of the centre to add a decoration to Coram's Christmas tree.
The Queen came to the aid of eight-year-old Shylah Gordon-Clarke as she struggled to add her own decoration to the tree.
Shylah's mother Evie Clarke is part of Coram's Young Parenthood Programme.
One decoration was a copy of Thomas Coram's coat and the other a red ribbon, representing the charity's museum.
Mr and Mrs Grant, who have supported the charity for a number of years, presented the event.
Mrs Grant said: "This is an issue that is very close to our heart. We have four children, three birth, one adopted, and they all have special needs.
"It's important for young people to know they are represented throughout society and to know that they are not alone."
Additional reporting by agencies
