A woman was screaming for help at a property where a one-year-old girl and a boy aged three were stabbed to death, a neighbour has said.
Police and the air ambulance were called to the home in Aldborough Road North, Ilford, east London, on Sunday evening after reports of a man and two children injured.
The toddler died at the scene while the boy died in hospital, Scotland Yard said.
A 40-year-old man, who was known to the children, was taken to hospital for treatment.
A murder investigation has been launched although police are not looking for anyone else over the killings.
A mother-of-two who lives across the road and gave her name as Reshna said:
I heard a woman screaming 'Help me'. I knew something horrible must have happened, it went on for about 10 minutes.
The neighbour said she later saw medics carrying a "little body" in a bag outside.
My heart just sank, it's devastating, horrific. From a mother's perspective ... I'm still shaken from it, I can't imagine what she feels at the moment.
Police were seen patrolling a cordon around two newsagents attached to some flats in the quiet residential road off the A12 on Monday morning.>Officers were overheard talking about getting CCTV from one of the newsagent shops.>A person who lives in the road said she heard someone "screaming and screaming inside" before police turned up and officers went "rushing in".
The air ambulance came and that's when I knew it was serious, that something nasty had happened. It has absolutely shook me, I couldn't sleep last night. I knew something terrible had happened but when it came out that two children had died, I was shaken.