Singaporean Chloe Choo, 11, has grown up with the musical The Sound Of Music in more ways than one.

In 2014, she auditioned for a part as one of the von Trapp children in the musical and was successfully cast as Gretl, the youngest of Captain von Trapp's seven children.

The musical tells the uplifting true story of Maria, a fun-loving governess who changes the lives of the widowed von Trapp and his children by reintroducing them to music.

Earlier this year, Chloe auditioned again for the same musical.

Out of more than 400 children here who auditioned for the musical's roles for children, Chloe was one of the 18 successful ones picked.

This time, she plays Brigitta, one of Gretl's older sisters whom she describes as "a smarty-pants".

Still, she finds herself looking out for the other children playing Gretl for this season of The Sound Of Music. The international production is playing at the Mastercard Theatres at Marina Bay Sands.

"They are so cute. Watching them reminds me of the time that I played Gretl. I was just eight years old then," she says.

Fellow cast member Samantha Lee, 12, who was born here, but whose parents are Australian, feels the same way. She was also a part of the musical's cast in 2014.

"I played Marta when I was nine. Now, I play Louisa, who is older and more mature. I feel that I've grown up with the show through the characters I play," she says.

The auditions were a gruelling process that took three days and saw the young hopefuls being assessed on singing, dancing, acting and harmonisation skills.

Cuts were made along the way.

Samantha says: "Elimination rounds are nerve-racking and there is a lot of crying after children are told to go. Everyone is there because they want a part."

The final 18, whose ages range between seven and 15, were informed of their success in clinching a role in June this year.

Rehearsals began last month. The children had to practise every day except on Sundays and for four hours each session.

Even though the rehearsals require time and commitment, Samantha says she enjoys going for them because that is where she gets to learn all the songs and dance moves.

What, in her opinion, does it take to be a good performer?

"A good memory, good psycho-motor skills, good improvisational skills and spatial awareness because we have to be aware of where we're supposed to stand and react accordingly if someone's in the wrong place," she says.

For the young actors, one of the most challenging parts of the show is the quick costume change at the end of Act Two, where they have to switch from casual to formal wear in just 14 seconds.

Because the show centres on music, there are scenes in which the singing needs to be energetic and where harmonisation is key.

Chloe says such scenes require "great concentration" because each child is singing a different part and there are times when they change parts within the same song.

Focus, as well as the "good psycho-motor skills" Samantha refers to, are also needed in scenes in which the children have to sing, march and keep a beat, all at the same time.

The musical's resident director Frank Thompson says: "Children bring great energy to a show."

Still, as with any professional production, there are rules to follow.

Cast member Max Makatsaria, 10, who holds American-Russian citizenship, knows that he is not allowed to eat in his costume and that he has to be punctual for rehearsals and have a positive attitude. "I also need to be respectful of everyone, if not the adults won't like us or be impressed," he says earnestly.

With the show in full swing and the start of the school holidays, the children are thrilled that they get to sleep late and do not have to go to school.

They are bracing themselves, however, for when the show draws to a close next month.

Max says: "I will definitely cry and I'm going to be sad. Because I now have a routine and that will soon be missing from my life."