Some of the children are barely out of diapers, yet they will soon be performing at the New Orleans Jazz & Heritage Festival.

A key part of a recent Sunday afternoon rehearsal at the Donald Harrison Sr. Museum was to set the children at ease. “You’ve been on the stage before,” said Roslyn Smith, 66, looking directly at Jefferson Smith (no relation), 6, one of the seasoned veterans of Young Guardians of the Flame, a youthful spinoff of Guardians of the Flame, one of the city's black-masking Indian tribes that are often referred to as Mardi Gras Indians.

Like the school principal she used to be, Roslyn Smith spoke with authority. She was recruited to help lead the group by Guardians of the Flame’s Maroon queen, Cherice Harrison-Nelson, 59, a former teacher of Smith’s at Oretha Castle Haley Elementary School on North Robertson Street.

On Saturday, Jefferson will perform for the third year. “So you know when it is your turn, everybody will be listening to you and looking at you,” Roslyn Smith told him. “You wait for your name. It is your turn when I say, ‘Jefferson! Play your drum!’”

The instructions were old hat to Jefferson, who wiggled around on his chair while Roslyn Smith talked. But when his name was called, he came to life, strapping his drum on his shoulder, running to center stage, hitting the drum firmly with one hand, while he held it against his hip with the other.

His father, Jermaine Smith, watched intently from the museum yard: “He now knows what’s expected. He just kind of flips on a switch,” he said of his son, who came to the stage leading one of the group's newest members, baby brother Abel, 3.

The group ran through the drum solos, sang songs and listened to Indian chants from Big Chief Clarence Delcour, 71, of the Creole Osceolas. Then one of the youngest Young Guardians, Ezra Levine-Harrell, 3, ran to Roslyn Smith’s lap — and fell asleep.

No culture can be perpetuated without some naptime, said Harrison-Nelson with a laugh, as she scanned the proposed set list.

“Scottlyn — are you confident doing “This Little Light of Mine?” she asked six-year veteran Scottlyn Marquez, 13. Scottlyn seemed unfazed, but her mom assured Harrison-Nelson that they’d run through the song at home.

The rehearsal was called so that the group could run through its Jazz Fest set. Harrison is coordinating white, hand-sewn outfits and feathered headdresses for the performance, which will include traditional spirituals from the African American tradition, short explanations of history and culture by Harrison-Nelson and drumming, dancing and singing from the black masking Indian tradition.

But the gathering wasn't just about rehearsing, though. After the youngsters climbed the broad set of stairs to the museum’s stage, they made a beeline for Herreast Johnson Harrison, 81, Harrison-Nelson’s mother. A former nursery school operator and widow of Big Chief Donald Harrison Sr., Herreast Harrison is known for showering Young Guardians of the Flame with love and an endless supply of books, part of a youth-literacy tradition continued in honor of her husband, a voracious reader.

The education and culture genes run strong in the Harrison family. Though she’s now retired, Harrison-Nelson spent her years in the classroom teaching the culture and history of New Orleans; her jazz studies curriculum has been widely used across southeast Louisiana. She has natural connection to the topic: Both her brother Donald Harrison Jr. and nephew Christian Scott are well-known jazz musicians.

Nearly 30 years ago, when Jazz Fest first hired the group to play in the Kids Tent, it included several of Donald Sr.’s grandchildren: Harrison-Nelson’s son Brian Nelson, nephews Kiel and Christian Scott and niece Victoria Harrison.

Today, the next generation of Young Guardians group includes Smith’s grandchildren, Niccolas Smith, who’s 8, and Ariya Smith, who just turned 6 and has been masking Indian and performing with the Young Guardians before she could walk. It’s now central to her identity: She wanted to wear her Indian suit on her sixth birthday — until it became clear that the feathers and finery wouldn’t survive the party’s bouncy house.

Other members of the group are trying to puzzle out their identity, through the Guardians. Sherrie DeVore’s grandchildren Dakota Dillon, 7, and Gregory Johnson, 8, who just joined Young Guardians earlier this year, have a great-great-grandmother who was Choctaw Indian, and they know that the African American communities where Mardi Gras Indians originated also had ties to Native Americans.

“So this is a really good opportunity for them to learn about their heritage all around,” said DeVore, as she sat in a folding chair on the museum lawn watching rehearsal.

As DeVore’s grandkids finished solos that seemed especially polished for first-time Jazz Fest performers, Roslyn Smith gave them a look of proud approval as she wrapped up the day’s rehearsal. “You are going to be stars,” she said.

Harrison-Nelson opened a cabinet at the edge of the stage and handed out a shiny new book to each Young Guardian.