The phone call from New York came in mid-October.

Could the Moorestown Theater Company stage a world-premiere workshop production of a new children's musical - before Christmas?

"We knew there were a lot of hurdles to clear, but we do that every day with every show," says director Mark Morgan, noting that MTC has 94 shows to its credit.

Music Theatre International, which licenses productions of adult and junior versions of Broadway musicals, asked MTC to stage The Magic Tree House: A Ghost Tale for Mr. Dickens, Jr. "as a favor," Morgan says.

"It's kind of like the old days, when Broadway shows would try out in Boston or Philly," he adds. "We've never done a world premiere. And it's pretty cool."

Written by Jenny Laird and Will Osborne, with lyrics by Osborne and Randy Courts, and music by Courts, the musical is based on the popular Magic Tree House books by Osborne's wife, Mary Pope Osborne.

A synopsis: Jack and his little sister, Annie, travel through time (with the help of Merlin) to 1842 London, where they encounter Charles Dickens, Tiny Tim, Oliver Twist, Queen Victoria, and other characters from fiction and history.

The MTC's production opens Dec. 20 and "is all from scratch," says Morgan, 53, a father of three who lives in Moorestown. The company has presented more than 60 performances of 15 shows this year; Elf Jr., now in its final week of rehearsals, opens Saturday.

Morgan founded the nonprofit company a dozen years ago after a career in sports information, and is fond of saying that musical theater is a team sport. But with The Magic Tree House, his players don't know the plays. Much less the play.

"There are no cast recordings. There are no videos," says Morgan. "They sent us a script, and then a second [revised] script. But I've told the kids: 'You'll be creating this.' "

Nearly 50 cast members, ages 6 to 17, are learning lines, dances, and songs in the basement of First Baptist Church of Moorestown, where MTC has office and rehearsal space. Saturday's rehearsal, the third of a dozen, was four hours long.

I watched as these exuberant youngsters ("theater kids aren't shy," Morgan notes, accurately) run through the show's catchy opener, "Christmas in the Air."

"This is a number where there's a lot going on, and this is where you'll end up at the end of it," choreographer Kaitlin Tumulty, 28, tells her dancers. She's done nearly 50 MTC shows.

Later, during a break with her assistant choreographer, Lizi Baldwin, Tumulty, who also lives in Moorestown, also notes there are no videos or DVDs of this show available for inspiration. She and Baldwin are making dances on "a totally blank canvas," Tumulty says.

The energy and enthusiasm of the cast are invaluable.

"They're not afraid to try new things," says Baldwin, 22, a Richard Stockton College health-science major from Delanco.

Down the hall, Morgan's wife, music director Carol Ann Murray; her mother and accompanist, Mount Laurel resident Beverly Bennett; and assistant music director Jackie Gonzalez are singing lyrics over the instrumental tracks of the show's 11 songs.

The trio reads from sheet music and sounds great. The resulting vocal-added tracks will be distributed to the cast to help them master the tunes.

"Usually, it's the kids who are hearing the songs for the first time, but we're also hearing them for the first time," says Gonzalez, 30, of Medford, who teaches music in Mount Holly elementary schools.

Many of the cast members are MTC veterans, including Morgan's daughter Juliet, 11. She made her theatrical debut as an infant in MTC's debut production of Annie.

This time Annie is her character's name, and she's playing opposite another MTC veteran, Ryan Coggan, 14, of Hainesport.

"People think [theater] is all fun and games," the Rancocas Valley Regional High School freshman says. "Of course it's fun. But it's also hard work."

I'll say. The kids get occasional two-minute water breaks and a more extended break two hours into the rehearsal. But I can tell they're jazzed to dance, sing and act together, and to put on a show no one's ever seen.

Break a leg.