This weekend’s Christmas concerts by the Island Community Chorus, directed by Peter Boak, will be unlike any in the group’s 20-year history. On Saturday evening and Sunday afternoon at the Old Whaling Church in Edgartown, the 125-member choir will be joined by more than two dozen much younger voices as the Martha’s Vineyard Children’s Chorus makes its holiday debut.

“The children’s choir is only a year old,” Mr. Boak said, after rehearsing the adult chorus in the church Monday night. “At their first public concert last spring, at Union Chapel, they invited the community chorus, the high school Minnesingers and the high school mixed chorus, so the kids in the children’s chorus had something to aspire to, to see what happens through a lifetime of singing.”

At the spring concert, each group performed a couple of numbers before joining in a mass choir to sing with audience participation. “That was a really wonderful experience,” said Lisa Varno, 31, founder and director of the children’s chorus. “When we all sang together, we invited the audience to sing an ostinato underneath us. It sounded so beautiful in that space.”

For the first time, children's choir will join the community chorus. — Mark Lovewell

This fall Ms. Varno asked the community chorus if the children could join them for the holiday concert. Mr. Boak’s response was immediate.

“That will be great,” he said.

The young singers range in age from first grade to seventh grade, and Tuesday afternoon was their first rehearsal in the Old Whaling Church. Lining four pews in front of center stage, they wriggled, stretched, jumped and spun in place as Ms. Varno led a brisk set of warm-up exercises to get them feeling comfortable in the vaulted, high-windowed church.

“Trust that the space is going to hear you,” Ms. Varno told the young choristers, who are in just their second semester of singing together. “It’s a bigger space than you’re used to, but you’re certainly filling it.”

Unaccustomed to public performance and a little at sea in their grand surroundings, they watched Ms. Varno carefully as she demonstrated proper concert posture.

Choir is made up of kids from first to seventh grade. — Mark Lovewell

“I’m going to show you some funny things, so be prepared to laugh,” she said, before mimicking an attentive audience member sitting upright and paying attention, and then a squirming child in the chorus. She also slouched languidly across the aisle, leaning on the edge of a pew, to show them improper posture. “If I conduct like this, you’re welcome to stand like this,” she said with a smile.

Humor and light-heartedness are hallmarks of Ms. Varno’s style as a chorus director, a job she has held as a public music educator for nine years in Massachusetts and Pennsylvania. She also has deep Island musical roots; her mother and aunts sang with the high school Minnesingers. Ms. Varno formed the Martha’s Vineyard Children’s Choir in January, 2016, in part as a “feeder program” for the Minnesingers but also because there was no Island-wide singing group for kids.

“I really thought, there’s a gap here, and that it would be useful for the community, so I decided to take it upon myself to start one,” she said. Rehearsals are weekly, and auditions are non-existent.

Lisa Varno started the children's choir a year ago. — Mark Lovewell

“I would like it to be inclusive and community-driven,” she said.

This weekend’s concerts, Saturday, Dec. 3 at 7:30 p.m. and Sunday, Dec. 4 at 3 p.m., will feature the children’s chorus in half of the 12 numbers on the holiday program. The children will sing three songs on their own and three with the Island Community Chorus: I Saw Three Ships, Petit Enfant and a stirring, modern version of Away in a Manger, arranged by the young Norwegian composer Ola Gjeilo.

“The acoustics are just so beautiful,” Ms. Varno said of the Whaling Church. “I could tell they were so excited to be singing in that space. It’s like you have a whole new voice when you sing in a space like that.”

The young singers will take their seats for six songs and carols by the adult chorus, including a lively 5/4 rendition of We Three Kings, arranged by composer Russell Robinson in the style of Dave Brubeck with a cool wordless riff.

The concert program runs just over one hour. Intermissions “really break the moment,” Mr. Boak said.

Choral music continues at the Whaling Church on Dec. 9 and 10 with the traditional Christmas in Edgartown Minnesingers concerts on Saturday at 8 p.m. and Sunday at 4 p.m. The Children’s Chorus will again be making guest appearances, as will Santa Claus after the Sunday matinee.