A woman has been arrested on suspicion of murdering her two babies just days after the family moved into a £1.2 million home.
The 10-week-old boy and his 14-month-old sister, Lily Sky Boots, were discovered unconscious by their father, Jeff Boots, when he returned home from work, sources said.
Police arrested their mother, Felicia, at the semi-detached home in south-west London after emergency services were unable to revive the children at the scene.
Detectives suspect she smothered the babies while suffering from post-natal depression. Mrs Boots, who is in her 30s and is a trained hairdresser, had been busy completing removal from a nearby penthouse apartment in the weeks before the deaths.
Both Mr Boots, an investment banker, and his wife are understood to have moved to the UK in the last few years from Canada.
Neighbours of the couple's new three-storey home, which boasts a 45ft back garden near Wandsworth Common, said the family seemed "very nice".
Locals also confirmed that the couple featured in pictures on Facebook showing them smiling together under an umbrella.
Jackie Cook, 52, said it was too early to have known the couple well. She said: "It's such a tragedy, I can't believe it. Last night there were police swarming everywhere. There were ambulances and police cars all along the road. I think they only moved a couple of weeks ago."
The upmarket semi-detached property which the family moved into was recently sold by Savills estate agency for £1.2 million. Post arrived at the address for Mr Boots as forensic officers were seen coming and going from property, which was sealed off by a cordon with two officers standing outside.
Detectives from the force's child abuse command are leading the investigation.