A campaigner for mandatory reporting of child abuse says the NSPCC's proposal to make it a crime not to report known abuse "will protect almost nobody".
Jonathan West of the Mandate Now coalition of charities, said: "It is our opinion that the NSPCC proposal will protect very few children. To make it a crime merely to report known abuse will protect almost nobody, because abuse is very rarely known with certainty."
"Until an investigation has been carried out, all you have is a suspicion," Mr West added.
Mandate Now wants to go further than the NSPCC proposals by making it a crime to not report suspected abuse as well as known abuse.
David Cameron said "it may well be time" to change the law and make failing to report child abuse a criminal offence.
His comment comes after the NSPCC chief executive Peter Wanless said not mentioning abuse in order to save an organisation's reputation should be a crime.
Mr Cameron said at Prime Minister's Questions: "The Government is currently looking at that [changing the law] and of course both reviews will be able to examine this particular point and advise us accordingly. I think it may well be time to take that step forward."
The call by the NSPCC chief to change the law so that failing to report child abuse is a crime has been welcomed by a lawyer who represents 176 victims of disgraced TV presenter and serial abuser Jimmy Savile.
Liz Dux, a lawyer with Slater & Gordon, said: "The NSPCC's backing for mandatory reporting is a welcome and significant moment in our fight to protect future children from predators like Savile, Harris, Smith and Hall.
"This, coupled with an announcement earlier this week by Theresa May that an independent inquiry is to be held, signals we are moving in the right direction - the victims will take some heart.
"Universally the victims I work with say they want change, they support mandatory reporting.
"We must not pass up this opportunity to protect our children and we must not delude ourselves that outrages like these ones will never happen again - if we don't act they could."
The head of the NSPCC, who is leading a review into the Home Office's handling of abuse allegations, said failing to report crimes against children should be an offence.
Not mentioning abuse in order to save an organisation's reputation should be a crime, chief executive Peter Wanless told the BBC.
Mr Wanless's comments were "hugely welcome" and "a really significant U-turn for the NSPCC", the chief executive of the National Association for People Abused in Childhood, Peter Saunders, said.
The charity had previously said it felt "criminal sanction against those who hesitate is unfair".
A report written by NSPCC, the Royal College of GPs and researchers from the University of Surrey and University College London, states family doctors are ideally placed to spot early warning signs of child abuse.
The report states:
GPs should be given more responsibility to spot cases of child abuse to help prevent the "acute pressure" social services faces in dealing with the problems, a children's charity has said.
The NSPCC claims family doctors are often only seen as a referral service to pass cases along to social services.
However, GPs could do more to help children and families at risk if they were given more autonomy, time and support, they added.
The NSPCC said that GPs could contribute a new "public health approach" that could reduce the number of children needing to enter the child protection system.
The NSPCC has said that there were 8,077 children who were accused of sexual offences - 3,868 in 2012/13 and 4,209 a year later. Crimes included serious sexual assaults, rape and obscene publication offences. NSPCC chief executive Peter Wanless described the results as "deeply concerning".
Most victims knew their alleged abuser, with some of the most common crimes being teenage boys abusing female acquaintances, according to the NSPCC. It said most abusers were male though there was a small proportion of female abusers, and victims were male and female.
"We know that for many older children pornography is now part of life. Easy access to hardcore, degrading and often violent videos on the internet is warping young people's views of what is normal or acceptable behaviour.
Figures obtained by the NSPCC show more than 8,000 under-18s were accused of sexual offences against other children in the last two years.
The children's charity contacted 42 police forces across England and Wales with a Freedom of Information request asking for the number of under-18s who had been accused, the youngest victim and the youngest accused. Of the police forces contacted, four did not respond.
The youngest child to be accused was aged just six, while the youngest victim had not yet reached their first birthday.
Rolf Harris hid behind his "happy-go-lucky persona" while committing a string of sexual offences which damaged the lives of his victims, a children's charity has said.
The NSPCC received 28 calls about the veteran entertainer through its helpline, including 13 people who said they had been abused by him.
Speaking after the guilty verdict, Peter Watt, director of national services at the NSPCC, said:
Parliament must "recognise extreme emotional abuse" and give child protection services greater power by legislating against it, a senior member of the NSPCC said.
John Cameron, head of child protection operations, said the so-called "cinderella law" was not about punishing parents who did not buy their children "the latest gadgets or trainers":