At the Arden Theatre, a rich array of local acting talent is cultivating The Secret Garden, the Marsha Norman/Lucy Simon musical, innovatively co-conceived by Jorge Cousineau and company artistic director Terrence J. Nolen.

In the show, based on Frances Hodgson Burnett's 1911 novel, vocal powerhouses Jeffrey Coon, Alex Keiper, and Steve Pacek sing of illness, loneliness, and neglect in the setting of a gloomy Yorkshire estate in the early years of the 20th century.

Each Philadelphia thespian has showstopping moments of Celtic pop song. The staging concept conjures up delicate paper dolls and pop-up books, with miniaturized set pieces filmed and projected on a screen behind the actors, with cameramen and props people before them.

But the secret weapons of this show may be slightly higher-voiced. Bailey Ryon, 13 going on 14 and a native of Glen Rock, York County, plays Mary Lennox with a winning tenacity that makes the neglected garden blossom. Hudson Orfe is the tall-for-a-12-year-old from Titusville, N.J., who plays tart Colin Craven: His sickliness is The Secret Garden's plot pivot.

"Bailey more than keeps up with me," Pacek says about sharing duets with Ryon, last seen on Broadway in Matilda. "She was off-book before any of us, so we actually started out having to keep up with her - that's a pro." Pacek says he is impressed when he throws the young actors "something new, and it doesn't send them for a loop - they just react."

Hiring young actors brings special challenges, Nolen says. Someone might be perfect at casting - but between then and the show, voice and height can change too much. And then there's school. "If a young actor is cast, and his or her grades drop, I tell them they have to leave the show," Nolen says. "Can't let that happen. That's their future, maybe even more so than theater. They must be able to juggle school and this."

Ryon and Orfe manage to juggle it all. Both bounce between homeschooling and Arden tutors. And each has an arts hobby. Ryon's is dance ("I like sports, but they're physically impossible because, well, I'm just really bad at sports"). Orfe's is "piano and my studies in music theory."

Each relishes auditions ("though sometimes I get so nervous, my legs literally shake," says Orfe). Ryon is a grizzled vet who has been doing this since she was 3. "Sometimes, there's a weird show that I don't know why anyone would want to do it, but I'll go out for it anyway," she says. "I'm up for anything."

Some directors and casting-call teams aren't particularly nice or considerate. Not so the Arden team. "The Secret Garden audition was fun, and the director was really nice, which is not always the case," says Ryon. "Terry was calm, attentive, and not one of the people who stares down at their papers. I was calm because they were calm and the panel interested." Orfe says his legs didn't even shake this time out: "This audition was fine, and kind. I got a real chance to relax."

Orfe says the process has been so chill and open that, for the first time, he has been able to invest himself in a character and aid in its creation: "I haven't been able to live a character as such with other directors," he says. "With Terry, from the first line, I felt as I could live in Colin's shoes." Freedom gave Ryon space to improvise: "Terry always asks us to run scenes the way that we want to do it. It's nice to have input. He wants it to feel right for you and for him."

Height? It's a thing. "I'm surprised I got this part, as when I went to the audition, it was all smaller kids," says Ryon, a hulking 4-foot-8. Voices change. "When I went into the audition, I hit every note," says Orfe. "Time passed for the callback, and my voice cracked on an E."

"It's funny," says Ryon. "I have friends at school who think that when they get older, they're just going to jump into being in the movies. They don't realize the hard work that you have put in early on, how much you go through, from Equity rights to taxes, which are annoying. Trust me: It is hard, so just shut your mouth."