With a Laurence Olivier Best Musical award, one of British theatre's highest honours, under their belts, it is perhaps understandable that composers George Stiles and Anthony Drewe were initially reluctant to write for children's theatre.

Stiles recalls with a chuckle: "We were so busy at the time writing family theatre and other works. I never actually said 'Yes', Anthony agreed for us."

They have since done three musical productions, commissioned by the Singapore Repertory Theatre (SRT), for children aged two to six. The latest, The Three Billy Goats Gruff, is playing at the SRT's DBS Arts Centre till May 10.

Their first, The Three Little Pigs, which ran in Singapore in 2012, opens in July in the world's theatre capital, London's West End.

Mr Gaurav Kripalani, artistic director of SRT which commissioned the children's plays, says: "It's fabulous for us that a children's show is finally going to the West End and it'll have the SRT brand on it. We're going international." This is the first for an SRT- commissioned production and a big coup for the company, which has "struggled" to establish a name overseas, he adds.

Stiles, 53, says: "I was cynical about doing animal shows... but I'm so thrilled we said yes because it's taken off in a way we can't imagine."

He adds that the trilogy is travelling to places such as Sydney and Hong Kong, while animation deals are in the pipeline.

Speaking to Life! after a Saturday showing of The Three Billy Goats Gruff, he says: "It's such fun to watch an audience of kids who haven't set foot in the theatre. They come in, look around and are quietened by it. It's a collective experience."

Recounting how other earlier audiences were tickled by a simple gag at the current show, Drewe notes: "The things that kids find funny, you can't write into a script. It's one of the bonus things when it all comes together."

Stiles chimes in: "One rule we have is to have three 'suddenlys' on a page. It can be someone speaking loudly, a new character coming on or it starts raining."

Drewe promptly demonstrates: "Suddenly, there's a knock on the door. Suddenly, the troll comes out of his lair... it's like a page turner."

The duo met at university more than three decades ago, first as rivals and began collaborating on theatre productions in 1983. Among the productions on their resume is Honk!, which netted them a Laurence Olivier Best Musical award in 2000.

Now based in the United Kingdom, they have worked with veterans in the British arts scene such as prominent director Sam Mendes, theatre producer Sir Cameron Mackintosh as well as creator of popular television series Downton Abbey Julian Fellowes.

Drewe came to Singapore in 1997 when SRT's founding director Tony Petito invited him to compose lyrics for the production A Twist Of Fate. "I remember arriving for rehearsals one morning and we sat around the radio, listening to the news that Princess Diana was dead," he recalls.

Next up, the pair will hunker down in Drewe's house in south-western France, with only five weeks to write songs for another musical, Half A Six Pence. Their creative process is a back-and-forth one as they sit in adjacent rooms, volleying ideas and content to and fro.

"I write my lyrics on this large sheet of paper and my ideas for songs around the edges. Then I type it out and e-mail it to him, even though he's in the next room," says Drewe.

Stiles continues: "I start with the meter before going into the tune. For example, for Three Billy Goats Gruff, I wanted the troll to be less scary, so I gave him a part where he sings like Barry White... sometimes I build on some daft ideas."

One thing that they miss most about Singapore is how "audiences are so well-behaved here", says Drewe. "We love it. The parents come to the shows. They pay attention, applaud and, at the end, they come up to us and say 'thank you'."