Ben Johnston was irritated and frustrated and rightly so, he had thought.

It was most unjust, believed the 10-year-old, that his brilliant out-of-the-box idea of a backstage tour of the Opera House had been thwarted because of age. He'd have to wait until he was 12, for safety reasons, before he'd be allowed on the guided walk of Australia's most iconic building.

Father Christmas made up for it though sending him an impressive Lego set of the Opera House - the legendary man in red knowing just the right gift to put a smile on the face of a passionate young thespian and singer.

Ben didn't have time to open the box and start building until the end of March as the young soprano landed a role in the Children's Chorus of the Opera Australia production of Carmen at the start of 2014 season.

Carmen, of course, was playing on one of the most famous stages in the nation - the Joan Sutherland Theatre - in the country's most famous building, the Opera House.

Life's twists and turns had landed in Ben's favour and the Bulli Primary School student was excited that the stars had aligned.

Not only did Ben now get to soak in the backstage atmosphere at the Opera House, he also sat in the Green Room, among some of the world's most acclaimed performers, waiting for his own curtain call. As one of 14 children in the Carmen chorus, he was being paid for what he'd always done for free - sing.

"That's me in the middle with the drum around my neck," says Ben, pointing to the Opera Australia public relations photograph. "It was pretty cool to be the one with the drum."

It's even more impressive to sing in a professional opera company - an opportunity few singers ever achieve.

Ben and the chorus performed 23 shows over two months, with at least one night free between each performance.

At the end of the night, Ben would sleep in the car on the drive back to Bulli, arriving home at midnight. He'd attend school the next morning with his teacher giving him the grace of arriving late, at 10am.

"So he'd get a decent amount of sleep on those performance nights," explained mum Robyn Johnston, who was Ben's chauffeur and moral support.

Ben is now on to his second production for Opera Australia and is rehearsing for Mozart's pantomime The Magic Flute.

Ben plays one of a trio of spirits known traditionally as the three boys - although this year, for the first time, Opera Australia is using both girls and boys for the role.

The Magic Flute, which was Mozart's last opera, is a family-friendly production which awakens the magic of childhood and the world of fantasy.

Ben plays the third spirit and will sing the alto soprano role. He has a line to sing on his own. The three small spirits, who resemble miniature Mozarts with their white hair and costumes, are mythical creatures. Ben and the other spirits have to sing perched high on the shoulders of dancers. Even thought they will be harnessed, it's still no easy task, particularly in front of an audience of 1500 people.

"In the audition we had to practise singing on someone's shoulders in case our voice wavered as we moved," Ben says. "That was pretty cool."

There aren't too many children who have classical music on their playlist, but Ben has eclectic taste. He not only listens to classical music, but also likes other genres including musical ballads and contemporary pop. Guy Sebastian is his favourite artist.

"I like how he writes and sings his own songs," Ben says. "I'm learning the piano and am working towards being able to play and sing at the same time."

Ben began singing lessons at the age of eight with Carmel Lennard at Mt Pleasant and attributes much of his success to her.

He is currently being coached by singing teacher Karen Cummings at her Coledale studio. Karen has previously worked with children with roles in The Magic Flute and has been associated with Opera Australia.

"Ben's a really spontaneous performer and very musical," Karen says. "He communicates directly which is unusual for someone of his age. He doesn't have a lot of self-consciousness and has an incredible energy."

She said Opera Australia would have auditioned hundreds of children for both productions.

"It's not easy to get these roles," she says. "You have to be very musical because the harmonies and rhythms are complex. Ben is a soloist in The Magic Flute and it's actually a big deal to be singing a line on his own.

''But the atmosphere at Opera Australia is incredibly supportive for kids. They're not put under any pressure. It's a very nurturing environment."

Ben was in the vocal ensemble of Schools Spectacular and competed successfully in several eisteddfods over the winter months.

"I'm very proud of him," Robyn says. "Sometimes when we're at the Opera House it's hard to believe where we are and what he's doing there. Ben's very modest, but it's a great achievement for any performer."

When he grows up, Ben would like to be an architect or a musician.

"I like building and love to watch Grand Designs, especially the Australian version," he says. "Maybe I can do both - music and building."

Opera Australia's The Magic Flute is on at the Sydney Opera House January 2-30.