The National Society for the Prevention of Cruelty to Children does three things very well indeed. The first is campaigning, as evidenced by the government's announcement this month that it will ban smacking by childminders - a move the NSPCC has called for as a first step towards an outright ban on the physical disciplining of children, by anyone, in any form. The second is direct provision of services to children - helplines, abuse investigation services, and so on - as evidenced by its 180 projects across England, Wales and Northern Ireland. The third is self-promotion. The smacking ban was another chance for the NSPCC's press officers to call journalists, making sure that nobody missed the society's line. Indeed, 7 May, though it was supposed to be Children's Day, was more like NSPCC day.

The NSPCC raises people's hackles; to many critics, it personifies the nanny state, interfering in the home and family, meddling with parents' rights. It was already a "third sector" body, mixing charitable, campaigning and statutory work, long before new Labour thinkers seized on the model as a useful compromise between old-fashioned state bureaucracy and outright surrender to the private sector. Founded in 1884, years before the welfare state was established, the organisation had its own uniformed inspectors, colloquially known as "cruelty men", who would visit homes to follow up child welfare cases. By the time parliament passed its first child protection legislation in 1889, enabling the police to intervene on behalf of abused children, the NSPCC already had 32 local branches. In 1904, NSPCC inspectors were given the right to take children away from abusive families, and the organisation helped usher in further child protection legislation in the early 1930s. By 1963, its lobbying had resulted in laws giving local authorities the right to intervene on a child's behalf, one of the foundations of today's social services.

So why the enmity? The two roles - campaigning and lobbying on the one hand, providing services on the other - do not always coexist comfortably. Evidence to the Laming inquiry into the death of eight-year-old Victoria Climbie, criminally neglected by her great-aunt Marie-Therese Kouao and Kouao's boyfriend Carl Manning, accused the NSPCC, as well as four social services departments, the NHS and the police, of failing to protect the child. Staff at the NSPCC's Tottenham child and family centre had stalled on Victoria's case for a week and then decided to take no action. The organisation was thus placed in the position of calling for improvements in child protection while at the same time falling far short of its own standards.

Yet the NSPCC has also long been accused of exaggerating the extent of child abuse, notably in the early 1990s, when it claimed that satanic or ritual abuse was sweeping the nation. Dozens of children were taken from their families; police later found no evidence of abuse.

Then there are the charges that the NSPCC will do anything to raise funds. It spends just under 14 per cent of its £90.6m income on fundraising (just over 20 per cent goes on campaigning, public education and helplines; just under half on direct child protection and abuse-prevention projects), a figure that its officers say is comparable to what other charities spend. In the past, it has invested in arms manufacturers and, although a donation from Myra Hindley was very publicly rejected, it has taken donations of cash or in kind from the drugs company Pfizer and the oil giant Shell.

Frequently, the NSPCC is itself accused of exploiting children. It raises £2m a year from schools (an important target of its fundraising since 1891), and primary schoolteachers are currently being asked to run a "fair play day" to "promote fun sporting activities while raising vital funds for the NSPCC". Charities get the kind of ready access to very young children that toy and soft-drinks manufacturers can only dream of. "It's not fair," said a former school governor, "to use children's natural enthusiasm and concern to put pressure on parents to donate when they might not be able to afford to."

But the organisation's advertising tends to generate the most controversy. There was the claim that a donation of £2 a month could save a child's life. There was the 2001 poster campaign, showing a loving father leaning over his baby, with the strapline: "Later, he wanted to shake her like a rag doll"- but offering no helpline for adults or children who may have felt they were vulnerable. Its "Real Children Don't Bounce Back" commercial, showing a cartoon child being horrifically beaten by a real-life adult, generated 127 complaints to the Independent Television Commission. Again, other charities saw a confusion of roles. Was this prevention - an attempt to bring the risks of child abuse home to parents under pressure? Or was it fundraising - an attempt to shock viewers into opening their chequebooks? Yet the NSPCC can point out that the promotion raised hundreds of thousands of pounds, as well as putting hundreds of children in touch with help. And it was named commercial of the year at the British Television Advertising Awards.

The thread running through much of the NSPCC's work, like that of some other children's charities, is that child abuse is so horrific that almost any campaigning is justified if it gets the job done. The NSPCC's official aim, since March 1999, is to eradicate completely all forms of child abuse - smacking, shaking, even emotional abuse - "within a generation". What exactly does that mean? A generation is 20 years, says Mary Marsh, the NSPCC's chief executive since 2001, when she moved from the headship of London's Holland Park Comprehensive. But what emerges from her elaboration is subtly different from the slogan. "Clearly, you won't change human nature and some people will lash out," she says. "But what you can make sure is that as soon as something like that happens, there is immediate intervention." Her colleague Gerry Tissier, head of media relations, adds: "You can't change sin, you can't change psychopathology."

Whether this will satisfy the NSPCC's critics is another mat- ter. It may just confirm the views of one commentator on child protection who says: "Full Stop is a fraud - it is fundraising disguised as a prevention campaign." Those who argue that the NSPCC is silly to conflate smacking and baby-battering will be even less satisfied: critics such as the Times columnist Mick Hume quote the Climbie case as evidence that the NSPCC has fallen into the hands of zealots who are "so busy lecturing normal parents, and imagining signs of abuse in ordinary adult-child relationships that they cannot see murder being done in front of their faces".

The NSPCC, under Marsh, clearly listens to criticism and, while responding vigorously on occasion ("wrong, wrong and wrong again", Marsh replied to a Telegraph leader in February that attacked the organisation's spending on fundraising), it has also changed its campaigning approach. The latest posters show parents in distress because of their children's behaviour and, without accusation, calmly offers advice and support through the NSPCC's freephone number. Some critics see this campaign, sympathetically acknowledging the enormous stresses that parents can experience, as a significant step forward from its predecessors. "Previous campaigns," said one mother, "made things worse by demonising parents who aren't coping, and even exploiting their family's difficulties to promote the NSPCC."

Marsh has also reined in criticism of other providers of children's services. Yet the grumbling goes on. Council social service professionals feel that the NSPCC does only a small proportion of the country's child protection work, but gets all the credit.

The trouble is that, as some critics concede, the NSPCC sells itself and its cause very well. As a result, argues Gillian Thomas, author of a recent Demos pamphlet, the public debate on childhood is somewhat distorted, making it seem that every child lives in imminent danger of sexual assault or physical violence. But the NSPCC can hardly be blamed for trying to keep the public's eye on cruelty, even if it is now called abuse: that was what it was founded for. Perhaps like the McDonald'ses and Exxons of the corporate world, it has become a victim of its own success.