It seemed that Nelson Mandela's life, from prison on Robben Island to president of South Africa, had been documented from every conceivable angle. Yet on Friday came a fresh revelation that suggested you might never really know someone.

Mandela, 94, is an avid viewer of the reality TV series Toddlers and Tiaras. Or so his granddaughters claim.

Zaziwe Dlamini-Manaway and Swati Dlamini were promoting their own reality TV series, Being Mandela, which begins in the US on Sunday. In an interview with Associated Press they suggested that Mandela, world renowned as a liberation hero, statesman and Nobel peace laureate, "sort of likes" reality TV and will "definitely" watch their show.

"You'll be interested to know that he loves Toddlers and Tiaras," a laughing Swati said. Zaziwe added hastily: "Because of the kids! He just loves children."

Toddlers and Tiaras, shown on the TLC channel, is a documentary series about US child pageants. Its website states: "On any given weekend across the country, toddlers take the stage wearing makeup, spray tans and fake hair to be judged on beauty, personality and costumes. Toddlers and Tiaras follows families on their quest for sparkly crowns, big titles and lots of cash."

The programme is not to everyone's taste. Guardian columnist Lucy Mangan once observed: "The title is no exaggeration – many of the contestants in the Little Miss Glitz/Glamour/Gaggingly Vomitous parades are indeed toddlers. They are fastened into $3,000 rhinestone dresses, sprayed with tanning lotion, piled with hairpieces, fake nails and eyelashes and taught to strut, pout, preen, beckon and wink at panels of judges to compete for diamante tiaras, cash prizes and pageant immortality."

It seems an unlikely pastime for a man whose hinterland is known to include boxing and Handel and Tchaikovsky and who is said to read half a dozen newspapers a day, neatly folding them as he goes.

Ndileka Mandela, his eldest grandchild, denied any knowledge of Mandela watching reality TV. "I know he watches National Geographic and news channels but I don't know if he watches Toddlers and Tiaras," she said. "I've never seen him watch the programme."

The claim will do no harm to publicity efforts for Being Mandela on Cozi TV. South Africa's first black president, who was recently treated for a lung infection and had surgery to remove gallstones, does not feature in the series but the women's grandmother, Winnie Madikizela-Mandela, is said to relish making cameo appearances.

The granddaughters sought to allay fears that South Africa's most revered family is entering Keeping Up with the Kardashians territory. "We get asked this question a lot," Dlamini said in the AP interview. "Is this not going to tarnish the name and is this not going to be bad for the name? "But our grandparents have always said to us, this is our name too, and we can do what we think is best fitting with the name, as long as we treat it with respect and integrity."

The 13-episode first season follows the two women as they try to carry on the family legacy while juggling motherhood in Johannesburg.

The sisters, who spent most of their childhood in exile in the US, make a poignant visit to the prison where their grandfather spent 18 of the 27 years he was incarcerated by the white-minority regime. Swati has been working on publishing the prison diaries that her grandmother wrote but now cannot bear to read.

The sisters, along with two brothers, have become the latest famous names to launch a fashion line, called Long Walk to Freedom after their grandfather's autobiography, according to AP. They hope US audiences will see a vibrant and modern side of South Africa through their eyes.

"They also bicker. The family, especially Madikizela-Mandela, loves to gossip about when Swati, the single mother of a four-year-old daughter, is going to get married," AP added. "Swati is furious when Zaziwe, despite being sworn to secrecy, blurts to their grandmother that her sister is dating someone. Zaziwe, 35, is married to an American businessman and has three children."

The sisters are the daughters of Zenani Mandela and Prince Thumbumuzi Dlamini of Swaziland. They said their grandfather is "happy and healthy".