Two 9-year-old girls from London successfully flew above the skies of Gloucestershire to become the world's youngest formation wing walkers.

Cousins Rose Powell and Flame Brewer strapped themselves atop two of their grandfather's vintage biplanes and stayed upright as the planes flew just yards apart and reached speeds of up to 100 mph, according to the BBC.

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The girls come from a family of wing walkers. Flame's brother, Tiger, in 2009 set a record when he wing-walked with his grandfather at the age of 8.

In June, a professional wing walker, Jane Wicker, a 44-year-old mother of two, was killed in a fiery crash performing a routine maneuver at an air show in Dayton, Ohio.

Prior to the girls' flight, their grandfather, Vic Norman, who supplied the planes for the record-breaking stunt, downplayed any safety concerns.

"They're in a special little seat up there," Norman told reporters. "They're strapped in with a five-point harness. I think they'll be fine."

The girls decided to take on the challenge to raise money for Duchenne Children's Trust, a charity that provides research into Duchenne Muscular Dystrophy. Their friend, Eli Crossley, suffers from the disease.

"My cousin and I came up with the idea to be the youngest formation wing-walking team and wanted to help Eli together," said Flame, according to ITV News. "I'm really excited and a bit nervous at the same time."

"It's quite scary when you take off but if you like mega funfair rides I think you'll find the take-off really cool," Rose told the BBC, also calling the event a "once-in-a-lifetime" experience.