Written by Richard Tulloch and directed by Liesel Badorrek, The 26-Storey Treehouse play is an adaptation of the children's book by author-illustrator duo Andy Griffiths and Terry Denton, who penned the JUST! series and The Day My Bum Went Psycho.

The play follows the wild misadventures of Griffiths and Denton in their invention-filled treehouse. It features a mud-fighting arena, an anti-gravity chamber and an ice-cream-serving robot called Edward Scooperhands. Terry (Lilley) is the loose cannon who wrecks all of Andy's (Andrew Johnston) plans. Jill (Eliza Logan), whose character is based on Andy Griffith's real wife, has to rescue the boy duo from themselves and also from the conniving trickery of Hector Houtkop (James Lee).

"Every actor wants to play Hamlet," said Lilley. When Lilley graduated from NIDA, he never imagined it would be him on that stage in a pink skirt. "I couldn't even have imagined that last year," he laughed.

But dreams don't always go to plan. Lilley's younger self thought the acting world would be like drama school, performing Shakespeare's As You Like It and Chekhov's The Cherry Orchard. "When you're a young actor ... you're very earnest and very serious about your art and then you come to the real world and those opportunities are few and far between. So you get a bit of a wake-up call.

"Suddenly you have to broaden your range and you're doing voiceovers, you're doing puppetry, you're doing a show that involves dancing and singing or you're doing a kids' show."

Variety is something Lilley's co-star Johnston has also experienced. The self-described big kid, who still plays video games, loves performing as Andy for an audience of children.

"Kids are really great to perform for because they never laugh to be polite. They only laugh when they're genuinely moved by something," he said.

But besides children's shows, he's also starred in black comedy film Ad Nauseum, which he describes as "probably not the kind of thing you want kids to see". It contains a bare penis and other provocative images in a critique of the tactics advertisers use to get attention.

Johnston, like Lilley, didn't always envision children's shows for himself. At university, he was more drawn to Oscar Wilde, the naturalist movement and absurdism.

"There's probably a part of me, like every actor's darkest side, that wants to be receiving an Academy Award after age 35 and giving a speech at the Oscars," he said. "But I'm also just as happy to be swinging a banana around at the Opera House. It's pretty cool," he said.

The 26-Storey Treehouse is performed at Sydney Opera House  throughout January. It will be at the Melbourne Arts Centre Playhouse from April 8.

Ada Lee @adelinalee