Williams told the BBC that an "alarming" number of children were already behind bars. "I think compared to the rest of Europe we are in an obviously punitive frame of mind … [which] suggests that sometimes we don't really like them [children] very much," said the archbishop.
He added that there are lots of ways of getting tough on youth crime without throwing young people into jail for long periods. Instead of imprisonment, he recommended so-called "restorative" justice in which young offenders have to come face-to-face with victims and/or their families to understand the impact of their crimes, which, he says, could prevent further crimes.
But Londoners seem to be in no mood for cutting teenage knife criminals any slack, and the politicians have sensed the mood.
The city's new Mayor, Boris Johnson, told reporters: "Everybody is shocked by the level of violence we are seeing, particularly towards young people in London and we must work as hard as we can together to reverse this dreadful trend."
The Mayor's suggestions include airport-style metal detectors at train and subway stations, and tighter restrictions on drinking alcohol on public transport.
Already, police have begun a new, more aggressive program of searching anyone they wish at random, without having to justify their suspicions.
An unarmed Community Police Support Officer, who gave her name only as Cass, told ABC News: "There is definitely an increase in knives being found on kids, and maybe that is because police are now searching teens more often now."
She added that teenage gangs often show up on the buses she and fellow officers patrol.
"You get up to 20 on a bus at the same time," she said. "And that's where we come in. We safety officers get on the bus and they are less likely to do anything."
Johnson said he wants police to do "more intelligence-led police initiatives focused on key estates, more handheld scanners and knife arches to detect guns and knives and a huge drive to get kids off the streets and into activities which raise their aspirations and help turn their lives around."
Poverty, sub-standard education, lack of public facilities, and broken families all contribute to the gang culture, teen experts say.
"They get sucked in when they're about 15, "Cass explained. "They want to be in a gang. They'll say 'oh, that's really cool, lots of bling, fake jewelry.' There is no father around for a lot of them, no father figure, and they see the gang as like a family. And to prove themselves to the family they start by doing a little damage with a knife, then they might go further and it escalates until someone is suddenly dead."
Some experts on youth crime warn that most of the new crackdown measures may not work, and amount to little more than political posturing.
"I'm skeptical about whether the latest measures will have an effect," Enver Soloman, deputy director of the Center for Crime and Justice Studies at King's College London, told The Associated Press.
"The clear message from research is that kids carry knives because they don't feel safe," Soloman said. "Unless you address that feeling of insecurity, you are not gong to have a big impact on the number of kids carrying knives."
By the way, Romeo Peacecraft, the 15-year-old who narrowly escaped being stabbed, moved to London two years ago from Dallas, Texas.
"I know that the U.S. has a reputation for violent crime," he said. "But London is where I, and other kids, feel unsafe."