Police and paramedics discovered the 37-year-old woman and five-year-old boy in Brookside South, Barnet at 1.37pm on Tuesday but were unable to save them.
Murder squad detectives continue to question a 37-year-old man who was arrested on suspicion of murder. He is known to the Chinese family.
The mother is the 15th woman killed in an act of violence in London so far in 2022 – a third of the 46 homicides being investigated by the Met, British Transport and City of London Police.
The ratio is higher than the same time last year, when 13 out of 58 victims were female.
Forensics officers on Wednesday trawled for clues and requested doorbell camera and CCTV footage in the affluent street where homes fetch upwards of £800,000.
One neighbour said: “They seemed like a perfect family.
“We saw the mum taking her two boys to the local school every day. She was always smiley and we just cannot believe what had happened.
“This is a very quiet neighbourhood. The first I knew of what was happening was the air ambulance laving nearby. We are all horrified by what has happened.”
Another resident added: “It’s a nightmare – the last place you would imagine this happening. “They are a quiet family at that house, nothing untoward at all.”
A third added: “They are such low key people in that house you wouldn’t know they were there. They are extremely private – the kids have been at local schools. We are devastated that this has happened on our community.”
A mother-of-two said the deaths had left her feeling scared.
Becky, 39, who did not give her last name, said of her neighbours: “Oh my God, it’s just shocking, it really is.
“Yes, I knew the family, nice, quiet Chinese family, from China. I’m bad with names.
“I’m a mother of two girls, similar age (to the child victim), they have never played but they have met them before.
“I have cried so much, earlier in particular when I heard that a child was involved, that was devastating.”
Mother-of-two Rummana Chowdhury, 37, said: “I don’t know them, it’s definitely very sad, it’s shameful.
“I can’t believe this, it’s unbelievable.
“It’s scary and sad as well because this morning everything was OK and suddenly this happened.”
Chief Superintendent Sara Leach, the Met’s north west policing commander, said: “The whole community will be shocked and saddened to hear of this terrible incident.
“Our thoughts are with the family and friends of the woman and child who have died, and also with the officers and paramedics who were first to arrive at what was an incredibly challenging scene.
“Specialist detectives are working to establish what took place and a man is in custody.
“While they are keeping an open mind as to what has taken place, I would like to reassure residents in the local area that there is nothing to indicate, at this stage, that anyone else was involved in this incident.
“I would urge anyone who saw or heard anything unusual earlier today, or in recent days, to come forward and speak to the police. Your information could be vital as the investigation moves forward.”
Information can call police on 101, quoting reference 3590/21JUN, or Crimestoppers anonymously on 0800 555 111.