Muslim children at risk of radicalisation at the hands of their parents are victims of child abuse and should be taken into care, Boris Johnson has said.
The Mayor of London called for children at risk from extremism to be removed from their families to stop them being turned into "potential killers or suicide bombers".
Mr Johnson said "fatal squeamishness" had developed over intervening in the behaviour of certain groups in society but insisted there was a need to be "stronger and clearer in asserting our understanding of British values".
Some children are being "taught crazy stuff" in the vein of the vile beliefs of soldier Lee Rigby's killers Michael Adebolajo and Michael Adebowale, he added.
In his weekly column for the Daily Telegraph he said: " We know that the problem of radicalisation is not getting conspicuously worse - but nor is it going away. There are a few thousand people in London - the "low thousands", they say - who are of interest to the security services; and a huge amount of work goes into monitoring those people, and into making sure that their ranks are not swelled by new victims of radicalisation.
" What has been less widely understood is that some young people are now being radicalised at home, by their parents or by their step-parents. It is estimated that there could be hundreds of children - especially those who come within the orbit of the banned extremist group Al-Muhajiroun - who are being taught crazy stuff: the kind of mad yearning for murder and death that we heard from Lee Rigby's killers.
" At present, there is a reluctance by the social services to intervene, even when they and the police have clear evidence of what is going on, because it is not clear that the 'safeguarding law' would support such action.
"A child may be taken into care if he or she is being exposed to pornography, or is being abused - but not if the child is being habituated to this utterly bleak and nihilistic view of the world that could lead them to become murderers.
"I have been told of at least one case where the younger siblings of a convicted terrorist are well on the road to radicalisation - and it is simply not clear that the law would support intervention.
" This is absurd. The law should obviously treat radicalisation as a form of child abuse. It is the strong view of many of those involved in counter-terrorism that there should be a clearer legal position, so that those children who are being turned into potential killers or suicide bombers can be removed into care - for their own safety and for the safety of the public.
" That must surely be right. We need to be less phobic of intrusion into the ways of minority groups and less nervous of passing judgment on other cultures. We can have a great, glorious, polychromatic society, but we must be firm to the point of ruthlessness in opposing behaviour that undermines our values.
"Paedophilia, FGM, Islamic radicalisation - to some extent, at some stage, we have tiptoed round them all for fear of offending this or that minority. It is children who have suffered."
Mr Johnson branded Islamic extremism as an "awful virus" but suggested political correctness was hampering attempts to stop it spreading.
He added: " It must have been dreadful for the family of Drummer Lee Rigby to listen to the ravings of his killers as they were finally hauled away to the cells and, one hopes, to a lifetime of incarceration.
"If those relatives have one consolation, it is that they were just about the last words those men will ever pronounce in public; the last time we will have to hear them pervert the religion of Islam - and the most important question now is how we prevent other young men, and women, from succumbing to that awful virus: the contagion of radical Islamic extremism.
" Every day in London and other big cities, there are thousands of counter-terrorism officers doing a fantastic job of keeping us safe. They have to work out who are the most vulnerable young people, who are the most susceptible - and they have to stop the infection of radicalisation before it is too late.
"That will sometimes mean taking a view about what is happening to them in their homes and families - and I worry that their work is being hampered by what I am obliged to call political correctness."