They shared their stories as part of a campaign launched on Thursday, aimed at trying to get Londoners to speak up if they suspect knife crime.
The Hard Calls Save Lives campaign hopes to inspire women whose close relatives may be on the fringes of knife crime to report information.
Becky Beston's 19-year-old son, Archie Beston, was stabbed to death in Kingston in February 2020 on a night out.
She spoke about a call she had to make as part of funeral arrangements.
"I had to call a complete stranger about getting Archie embalmed. You should never have to use those words with your son's name. Ever," she said.
"If somebody would have made that phone call, my Arch would be here now."
Lorraine Jones's 20-year-old son Dwayne Simpson was stabbed to death as he tried to save a friend's life in Brixton in 2014.
She said: "I'd just come back from a busy day when the door rang.
"It was one of Dwayne's friends.
"He said, 'Dwayne's been stabbed, come quick!' It was like I was in another world. I felt lost.
"I had to call my mum. It was the hardest call - I was out of breath and my stomach was tight.
"Even when I was making a call my hands were shaking. I tried it three times, I was just so helpless and weak.
"I had 20 wonderful years with him, and really good memories. But I didn't realise the impact he had until he passed away."
The campaign is targeted at people in areas affected by violent crime.
It is particularly aimed at inspiring women whose children, siblings, nephews or nieces may be on the fringes of knife crime to make a report if they know someone who carries a knife or where a weapon has been hidden.
Lillian Serunkuma, whose 15-year-old son Quamari Serunkuma-Barnes was knifed to death outside his school gates in 2017, recalled calling her aunt to let her know he had been stabbed.
"She just screamed. That was the hardest thing about that day," she said.
"It can be hard to make the call to say someone is involved in knife crime, especially if it's someone you know or love.
"But it's so much harder if you don't.
"It's almost as bad to lose a child or a friend to prison as it is to lose them if they're killed. Either way, they're going to suffer as a result of knife crime."
Yvonne Lawson, whose 17-year-old son, Godwin Lawson, was stabbed to death in 2010, said she rang her sister after she was told he had died.
She said: "I just kept repeating 'died, died, died'. Godwin was stolen away from us in such a terrible way.
"My family is broken into pieces, just missing him.
"We didn't even get a chance to say goodbye, and he's never going to be there, he's never going to be part of us anymore.
"The least we can do is use his memory to change lives."
And Jean Foster, whose son Christopher Foster, 34, was stabbed to death outside a London pub in 2010, said: "They told me Christopher had been murdered.
"We called nine or 10 times. Slowly, we came to the realisation that he was never going to call back.
"People may think that keeping quiet keeps you out of their focus, but it empowers them.
"No one is safe if we keep quiet."
Metropolitan Police Commissioner Dame Cressida Dick hopes their "tragic accounts" will encourage people to anonymously call Crimestoppers.
She said: "We understand this is a difficult thing to ask - but you don't have to name names and even a small piece of information could be vital.
According to Met Police data, there were 126 murders in London last year, down from 151 the previous year.
London had the highest volume of knife crime in England between October and September 2020, according to the Ben Kinsella Trust.
Despite pandemic enforced lockdowns, there have been several fatal stabbings in London.
On 1 April, 23-year-old Reece Young was stabbed to death at a vigil in memory of another knife attack victim in Croydon.
In 2019, home secretary Priti Patel announced that the police will be given an extra £35m to tackle violent crime, with £7m given to the Met Police.
Today, Thursday, 8 April, the mothers will join Commissioner Dick at a socially distanced event at New Scotland Yard where their films will be screened.
Crimestoppers can be contacted anonymously on 0800 555 111 or at Crimestoppers-uk.org.