Four children were treated for carbon monoxide poisoning after their grandmother brought a barbecue indoors to dry her washing.
The woman, who has not been named, lit the device which she set up in the family kitchen before leaving the house.
Her daughters-in-law were in the house with her grandchildren, two of whom were asleep upstairs.
Her three-year-old granddaughter collapsed when she was overcome by the deadly gas later that afternoon and was treated in hospital with five of her relatives.
They included two boys aged two and 10 months, a four-year-old girl and the woman's two daughters-in-law, aged 26 and 29.
Firefighters were called to the home on Hockley Avenue, in East Ham, east London, on Wednesday afternoon, soon after the grandmother set the barbecue alight.
All six have now been discharged from hospital.
Fire chiefs branded the grandmother's behaviour dangerous and campaigners warned of the hazards of bringing barbecues indoors.
Dave Brown, of London Fire Brigade, said: "In my 28-year career I have never heard of anybody using a barbecue to dry clothes let alone using one indoors.
"Never, ever bring a lit or smouldering barbecue indoors. Not only is it a serious fire risk but it also emits carbon monoxide which is a poisonous gas that can kill or seriously injure."
Earlier last year, six-year-old Isabelle Harris, from Gosport, Hampshire, died after her parents brought a disposable barbecue into their tent to keep warm during a break in the New Forest in April.
The schoolgirl was one of a number of campers killed by the gas last year.
The Department of Health believes 50 people are killed by the gas each year, while at least 4,000 are treated in hospital.
But this figure is likely to be much higher because of difficulties surrounding the diagnosis of CO poisoning.
Symptoms are often similar to common illnesses like flu and food poisoning.