Fundraiser Max Woosey and charity worker Sahil Usman were among those present.
A boy who raised money for charity by sleeping in his garden and a leukaemia patient who supported vulnerable people during the pandemic were among youngsters invited to the coronation.
Max Woosey, 13, known as The Boy In The Tent for his efforts, was seated inside Westminster Abbey with his father, Major Mark Woosey.
Having raised more than £700,000 for North Devon Hospice by sleeping outside for three years, Max received a British Empire Medal in the 2023 New Year Honours List for his service.
Speaking outside nearby St Margaret’s Church after the ceremony, he said: “It’s absolutely incredible meeting everyone.
“My dad’s like a textbook, so he’s been letting me know about all the military personnel.”
Asked what it meant for Max to receive an invite, his father said: “It was slightly surreal.”
Another teenager invited to the ceremony for his charity work was Sahil Usman, 17, from Blackburn, who nearly declined his invitation because he thought it was a hoax.
Sahil was diagnosed with leukaemia in 2018, and while still battling the disease during the pandemic, he supported around 300 vulnerable people in his community by creating gift hampers.
He said: “I was sent an invite by email, but I thought it was a spam email.”
Speaking about his family’s reaction to his invitation, Sahil, who lives with his mother and brother, said: “I thought it can’t be real, why would I get invited?
“My mum was really proud and convinced me that my invite was real.
“We’ve always followed the royal family, but the best part of the coronation is that a diverse community has been invited – this shows us the kind of King Charles will be.”
Sahil’s highlight of the ceremony was meeting the First Minister of Scotland Humza Yousaf.
Sahil said: “After we spoke, I was just going to take a selfie, but then he told me to bring my mum in the picture, that was a proud moment.”
Sahil was given the British Empire Medal in the 2022 New Year Honours List for his charity service.
Meanwhile some 400 young people were invited to watch the ceremony from St Margaret’s, next to the abbey, through their charity work, including Hana Saada, 18, from Buckinghamshire and Aniya Sofia, 18, from east London, who said getting a mention from the Archbishop of Canterbury during the service was an “amazing experience”.
Hana and Aniya are members of the National Citizen Service, a skills development programme for young people.
Aniya said: “When the Archbishop of Canterbury shouted us out, it was such an amazing experience, everyone was cheering.
“The fact that young people are at the forefront of this event was really nice to see.”
Asked what the monarchy means to her, Aniya added: “I think it’s important to celebrate the tradition.
“But then again, after hearing how a protester was arrested and considering the taxpayer money spent on today’s events, it makes me question whether these traditions are necessary in everyday life.
“I’m really grateful to be here and I enjoyed sharing this with other young people.”
Hana said: “I think young people definitely have different views on the monarchy.
“I’m hopeful that the King will continue to promote young people.”