“August Rush” director Kirsten Sheridan had reservations about casting 15-year-old Freddie Highmore in her film’s complex title role. August is a musical prodigy, a kind of transcendental figure on an unlikely quest to find his parents.

“In ‘Finding Neverland,’ (the character’s) mother is dying. Everybody remembers that scene where Freddie’s crying,” Sheridan says, describing the role that earned Highmore a Critics’ Choice Award and SAG nom. “I presumed I’d meet him and he’d be quite dark, whereas we needed August to have a lot of joy to counteract the hard stuff.”

Meeting Highmore in person, Sheridan’s reservations melted away.

“Freddie’s very open to life,” she explains. “He’s wise and centered in himself. He’s like a little Buddha.”

During pre-production earlier this year, Highmore told Sheridan exactly how he’d like to approach the lost-boy role. She told him to go for it.

“Freddie had this crazy idea that every time he picked up an instrument, he would let rip with (pure) joy in living,” Sheridan says. “He was so right. I think he could have directed the film himself.”

The Brit followed up “Finding Neverland” in 2004 with a formidable turn in Tim Burton’s “Charlie and the Chocolate Factory.” Johnny Depp, who worked with Highmore on “Neverland,” suggested him for the part.

Highmore recently completed “The Spiderwick Chronicles,” directed by Mark Waters, in which he plays twins Jared and Simon Grace.

“It was great fun to try and get the differentiation,” says Highmore, whose father, Edward, is an actor as well. His mother is a talent agent. Together, they’ve advised their son on his craft.

“You’ve got to try to get into the character — be angry if he’s angry,” Highmore explains. “Even if it looks odd going off and being upset in the corner, you’ve still got to do that.”

Recent breakthrough: November brings “August Rush” while “The Spiderwick Chronicles” follows next spring.

Role model: “Johnny Depp really stood out. He’s so normal, and yet he’s so famous.”

What’s next: “I’ve just done voiceover for ‘The Golden Compass’and finished the second and third installments (of Luc Besson’s “Arthur” series). Now I’m in the last year at school before I have these big exams. You’ve got to work for them a bit, you know?”