The young woman’s story begins: “I am 19 and the mother of two children.”

And who, on reading those words, can resist breaking off to do a little mental arithmetic? Yes, she was rather young when she embarked on parenthood. Which makes her one of those teenage mums we read so much about. And who, on realising that, can resist the temptation to judge this girl - let us call her Tanya - deciding, perhaps, that she is partly to blame for her situation and therefore should expect little from a society whose resources are better spent on more deserving cases?

Luckily for her, not everyone sees these things in black and white. Luckily for her and, more especially, for her children.

Because Tanya’s children might have been taken away from her, and either fostered or put into care. In fact, at one stage, it was looking a distinct possibility. But a charity stepped in and persuaded the social workers that she should be given the opportunity to prove herself a good mother. It set her up in a flat, talked her through depression and put her in touch with a group of young women in the same situation as herself.

She was given a telephone number she could call day or night, and she and her children were treated to days out. She was even shown how to keep her flat clean and tidy.

As a result, Tanya is now back in education. She has moved into a three-bedroom house, is a familiar face at tenants’ meetings, and has a good circle of friends. Most important of all, her children are not in care, nor are they with a foster family and possibly incubating the sort of emotional difficulties to which such arrangements frequently give rise.

Rather, they are being brought up by their own mother, who will hopefully see them through to adulthood and discharge them into the world relatively undamaged.

And the charity that made all this possible, that effectively prevented two children from going into care? Surprisingly for anyone who still associates the name solely with children’s homes, it was Barnardo’s.

It is 100 years since the death of Thomas John Barnardo: Dr Barnardo, as this Dublin-born son of an impoverished Prussian furrier styled himself, although he never completed his medical training.

He had intended to become a doctor, with the aim of joining the China Inland Mission and helping the poor in the Far East who were dying without knowing Christ. It was the desire to save souls that drove him from the moment of his conversion from agnosticism to Christianity at the age of 17.

Four years later, in 1866, it was the evangelical urge that inspired him to work with destitute children living and dying on the cholera-ridden streets of London’s East End.

Barnardo had moved to London to train as a doctor in preparation for the China mission. But so overcome was he by the physical and spiritual poverty on his own doorstep that all thoughts of travelling east were soon forgotten, along with his medical training.

In 1868 in Stepney, he opened his Juvenile Mission in a pair of adjoining houses: one for girls, the other for boys. Here, poor and vulnerable children were given free shelter, food, clothing and education in a pleasant if strictly regimented environment. Thanks in no small part to Barnardo’s flair for marketing, the Juvenile Mission was soon attracting generous donations and, before long, Barnardo had the support of the great philanthropist Lord Shaftesbury. Today, children in Years 5 and 6 are taught about the two men as part of the history curriculum.

At the time of his death in 1905, the “doctor” had 8,000 children in his care, half of whom were fostered while the other half lived in 43 homes and “cottage villages” around the country. He had rescued 59,384 children from destitution and often premature death, including abandoned babies and sick and disabled children, in line with his much publicised slogan: “No destitute child ever refused admission”.

Yet the road had not been smooth. There had been scandals, criticisms and litigation aplenty along the way, and Barnardo himself had been so vilified in certain quarters that his health suffered and he was forced to appoint trustees to help run his organisation. Much of this animosity was possibly a product of his overbearing manner. For as Winston Fletcher, chairman of the Royal Institution and a trustee of Barnardo’s, points out: “He wasn’t perfect.”

Mr Fletcher, whose book, Keeping the Vision Alive: the story of Barnardo’s 1905-2005, has just been published - launched by the organisation’s current president, Cherie Blair - compares the man with Sir Winston Churchill.

“Both were rather short,” he says, “both were fine writers and speakers, both were visionaries, both were workaholics, both were short-tempered, both were egotistical and both were known to bully to get their way.

“If he’d been a saint, I hope I would have said so. But he wasn’t. He had many human failings. But these were overridden by his achievements.”

Not least among these was the founding of a powerful brand name. As Winston Fletcher, who works in marketing, points out in his book: “There is no other large charity in Britain named after its founder, and precious few smaller ones.” Yet, as he goes on to say, many people still believe that Barnardo’s runs orphanages, something it has not done for three decades.

Roger Singleton has worked with the charity for 32 years and has been its chief executive for the past 22. He believes it was the experience of wartime evacuation and the emotional damage that children suffered as a result of being uprooted from their families that prompted society in general to rethink its views on how to help disadvantaged children, and Barnardo’s in particular to change tack so dramatically.

“Until 1945 to 1950, the important thing in caring for children was seen as looking after their material needs: clothing them well, feeding them well and making sure they were healthy,” says Roger Singleton.

“Only with the development of child psychology did people begin to appreciate that it was not only about physical well-being, but also about children feeling attached to, and wanting to be with, adults who mean a lot to them.”

From the first days of the Juvenile Mission, parents were obliged to relinquish their “rights” to a child before it could be taken into Barnardo’s care. “Barnardo basically believed in rescuing children from what he saw as being the evil and malevolent impacts of their family,” says Roger Singleton. “But our view is that, while some children can be quite unhappy and distressed at home, what they want is for the unhappiness and distress to end, not to be taken away from home. Therefore it’s a matter of trying to work with parents to seek to achieve that.”

Perhaps one of the most controversial aspects of the early Barnardo’s was its policy of “migrating” destitute children to Canada and Australia.

“Looking at it now, we shudder at the thought of sending children thousands of miles away,” says Roger Singleton. “But these things have to be judged by the standards of the time.”

By contrast, other aspects of Thomas Barnardo’s policies were radical by any standards, which frequently brought the organisation public opprobrium.

Notable among these was his colour-blindness (he took in children of every ethnicity), his acceptance of mental disability (his youngest daughter, Marjorie, had Down syndrome), and his policy of allowing unmarried girls to have one child out of wedlock (more than one was considered an encouragement to libidinous behaviour).

If one characteristic sets Barnardo’s, then and now, apart from some other charitable organisations, it is its refusal to judge the recipients of its charity, or to distinguish between the deserving and the undeserving. As a case in point, Barnardo’s recently organised a conference about young people who sexually exploit younger children.

“There are people who will take the view that you should castrate them or lock them up,” says Roger Singleton. “But if you take a humanitarian approach, these are young people in need, and if you don’t intervene when they are young, the problem will get worse.”

Today, the charity offers more than 350 services across the country, working with and campaigning on behalf of young people with problems relating to everything from drugs and mental illness to domestic violence and forced marriage.

Tanya is one of around 20 young parents in Cardiff and Newport being supported by the Marlborough Road Project, which Barnardo’s has run in partnership with a local housing association and Cardiff social services since 1992. Some receive help while continuing to live with their own parents, while others, like Tanya, are housed by the project and supported throughout their children’s early years.

In the minority of cases, where a child will clearly be in danger if left with its birth parents, the charity eases the transfer into local authority care, ensuring that children have sufficient information about their earliest years to enable them to come to terms with any future trauma. But as Sally Jenkins, children’s services manager at Marlborough Road, explains, the guiding principle of the project is that children should, wherever possible, grow up with their parents.

“That is obviously very different from what Barnardo’s did 100 years ago.

And in the short term, it is a million times easier to take a baby away and place them with ‘nice’ people. But so often they leave behind a young parent who is absolutely devastated because the family’s been torn apart.

And adoption is not a guaranteed success.

“All children deserve a chance to be with their parents and all parents deserve a chance to nurture their children to adulthood, and if we can provide that chance, that’s what we should be doing.

“I can understand that, when it comes to allocating resources, young parents who are possibly a risk to their children are not a popular choice, and politically it’s much easier to not provide or to cut services to teenage parents than to orphans. But what people forget is that, however they may judge the morality of teenage parents, their children should have the same opportunities as any other children.

“Dr Barnardo had a sense that people should have a chance. The way it was done in his day was very different from how we do it now. But the ethos - the idea that everybody counts for who they are - is not so different.”

Keeping the Vision Alive by Winston Fletcher is available from Barnardo’s shops, price pound;14.99, or visit www.barnardos.org.uk