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.
If someone consciously knows that there is a crime committed against a child, and does nothing about it because they put the reputation of the organisation above the safety of that child, that should be a criminal offence.
– Peter Wanless
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".