Six children, four mothers – and one father none of them has met. Meet the ‘family’ of Donor 66

They are all members of what they call the 66 Club, named in honour of the father they share – an anonymous sperm donor known only as Donor 66.

With their broad smiles, blonde or light brown hair and healthy complexions, there is an obvious resemblance even though they come from four different families.

The family: Back row, from left, Bree Ziegler, Justin Senk, Tyler and Mackenzie Gibson and Erin Baldwin. Front row, from left, their mothers Sherra Basham, Susanne Senk, Tina Gibson and Shirlyn Baldwin

Brought together thanks to a website, the six, pictured here with their mothers, know that they have six other half-siblings but they don’t know who or where.

They also know that by coincidence their father lives near them in Denver, Colorado. And they have some brief biographical details about him – he’s a blue-eyed, fair-haired man with five years of college education who works as a surgical assistant.

His children have been able to form their own loosely-knit extended family because their mothers logged on to the Donor Sibling Registry, which seeks to link the offspring of sperm donors. In America, unlike Britain, the anonymity of such donors is protected by strict regulations.

Susanne Senk, 54, and her husband visited the website after telling their son Justin the facts of his conception when he was 15. Justin, now 18, became curious about who the donor was. Mrs Senk said: ‘I can’t describe how amazing the feeling was when we looked up Donor 66 and found Rebecca Baldwin, who was five years older than Justin, and her twin sister Erin.

‘The next day we had news of more siblings – Tyler Gibson, the same age as the twins, and his sister Mackenzie, the same age as Justin. Justin had been an only child but overnight he had become one of a family of five siblings. It was unbelievable to see how alike they all looked. They even shared mannerisms.’

The following year, Sherra Basham realised that her daughter Bree Ziegler shared the same father. She said: ‘She feels it’s cool to be an only child who also has brothers and sisters. We manage to get together every three or four months. We usually manage some of the birthdays and we all do Christmas.’

The Donor Sibling Registry was founded eight years ago. Since then, some 22,000 people from a dozen countries including Britain have registered to try to find out whether they have brothers and sisters.