The 33-year-old woman and two boys, one aged five years and the other seven months, were found at 5.20pm on Thursday at a property in Kenton, near Harrow.
It is thought to have been a murder-suicide.
A spokesman for the Metropolitan Police Service said: "Officers were called at approximately 1720hrs on Thursday, 10 January by London Ambulance Service to an address in Woodgrange Close, HA3, to reports of a woman and two children with injuries.
"When officers arrived, the three were pronounced dead at the scene by medical staff.
"Next of kin are aware. The post-mortem examination for the woman is due to take place at Northwick Park Mortuary at 1500hrs on Friday, 10 January.
"Further details await in relation to other post-mortem examinations.
"Officers from the Homicide and Major Crime Command investigate. Detectives are not seeking anyone else in connection with the incident."
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