Children as young as six are carrying knives in the capital, Metropolitan Police Commissioner Cressida Dick heard as she discussed the devastating impact of the weapons with community leaders, victims and reformed gang members.
Ms Dick vowed to get to the root of knife crime as she visited a youth centre in Putney, south-west London, where she met the family of a young man stabbed to death last year.
The capital has seen a wave of knife attacks in recent weeks, with more than a dozen people left dead or seriously injured.
Earlier this month, Scotland Yard launched the latest phase of Operation Sceptre, its campaign to crack down on knife crime.
But despite more than 70 arrests over possession of offensive weapons and knives, within a week three more people had been fatally stabbed.
Meeting with community representatives at the Ashburton Youth Centre in Wandsworth, Ms Dick said the area has been "profoundly affected" by knife crime.
Three young people have been fatally stabbed in the borough in 2017, as many as the whole of 2016.
Ms Dick told them Wandsworth "is generally a safe borough, London is generally a very safe city", but she said the level of knife crime is "unacceptable".
But the commissioner was told violent attacks are becoming more frequent, and young people are carrying knives more and more often.
One woman told Ms Dick the issue is affecting children far younger than the teenagers and young men normally associated with carrying knives.
The woman said: "You are talking about teenagers carrying knives, but on the housing estate it's six-year-olds that are carrying knives, because they think they won't be stopped.
"You need to start there, in the primary schools - you need to tell much younger people."
The commissioner agreed the anti-knife message needs to reach much younger children, saying: "I am sure we - not necessarily the police, because we're not the best people often to give these messages, but possibly the police - we need to start at an early age."
Josh Osbourne, a mentor at the youth charity Carney's Community, said: "The feeling that I'm getting from a lot of the young people that I work with is a feeling of fear.
"They can't even cross the road because they're at odds or in a dispute with somebody else from literally the same postcode but across the road."
When Ms Dick asked him which age groups are affected, Mr Osbourne said: "From the age of as young as 10 or 11, from what I've witnessed, up until the age of mid-20s."