Brangelina: Price tag of $11m put on first pictures of the world's most famous children

From the hordes of paparazzi, camera crews and satellite trucks – and the security guards hired to contain them – it was obvious that a matter of great international importance was lurking within France's Lenval hospital.

But this was no medical breakthrough, no cure for cancer. The reason for the commotion? The birth of twins to one Angelina Jolie and her partner, Brad Pitt.

Called the world's most famous children even before they were born, Vivienne Marcheline and her brother Knox Leon, arrived into a world of scrutiny, tight security and a life already fraught with the perils of fame.

Jolie's French doctor, Dr Michel Sussmann, had tried to insist the 33-year-old actress was simply "a patient like any other", after she was taken in secret and by helicopter to the Nice hospital in late June from a luxurious 17th-century Provencal villa, where the "Brangelina" clan set up home for the birth.

But few expectant mothers are forced to take to the roof for a breath of fresh air to prevent causing a media frenzy and fewer still are able to sell the first pictures of their newly enlarged family for a reported $11m (£5.5m) to an unnamed American magazine. Like the first pictures of their biological child Shiloh, born in Namibia in 2006, the money is said to be destined for a charitable cause. The couple also have three adopted children, Maddox, Pax and Zahara.

"Everything is going well," Dr Sussmann said. "The mother, the babies, the father are doing marvellously well." He said the Caesarean operation was moved forward from its planned date "for medical reasons" so the babies could be born "in the best conditions". Pitt, 44, was at her side during the birth. Dr Sussmann said Vivienne weighed 2.27kg (5lbs) and Knox weighed in close at 2.28 kg.

The doctor added that he believed the baby girl's middle name was chosen in honour of Jolie's mother, actress Marcheline Bertrand, who died in January 2007 after a seven-year battle with cancer. She raised Jolie and her brother, James Haven, after divorcing their father, actor Jon Voight, when Jolie was a toddler.

Jolie is expected to stay a few more days in the hospital on the Promenade des Anglais waterfront drive, where her bright, spacious room on the fifth floor has a fine view of the Mediterranean.

News of the birth on Saturday night was broken by the local paper, Nice Matin, with Dr Sussmann saying the couple had decided this was how they wanted the story to emerge. He suggested this was a favour to the local paper, but thwarting the efforts of larger news organisations may have been in the couple's minds.

Last week, the hospital said it had coated the windows of Jolie's room with a special material to prevent paparazzi from taking unauthorised pictures of the star couple. Photographs in magazines and online that purported to show Jolie and Pitt in her room were fake, either manipulated or showing other patients, the hospital added. The name of Jolie's current film, Wanted, now feels more pertinent than ever for the star.

Nice was proud of its new arrivals. The Mayor, Christian Estrosi, promised that the twins would always be considered honorary citizens of the city, regardless of whether or not they take up French citizenship.

News of the celebrity births spread like wildfire in the streets of the city, where people were eager to offer their opinions. "Sleep when the babies sleep. That is definitely my main advice to them," said Nicole Stechmann, a visitor from Germany.

Actress's 'rainbow' family

The Brangelina clan now totals eight people with Vivienne and Knox, adding to Brad, Angelina and their four other children.

Maddox, Pax and Zahara were adopted while Jolie gave birth to Shiloh Nouvel in Namibia in 2006. The media interest in the birth became so intense that Namibia eventually revoked the visas of journalists sent to cover the story.

France's strict privacy laws may have made it a more attractive location second time round. Maddox, six, was adopted from a Cambodian orphanage in 2002 when he was seven months. Pax was born in Vietnam in 2003 and abandoned at birth. Jolie adopted the boy in March 2007 when he was three.

Zahara, three, was born in Ethiopia and adopted in 2005.

The new arrivals suggests a visit to a tattooist may be in the offing: Jolie has a tattoo giving the map co-ordinates of the places where all four of her other children were born.