A five-year-old boy and a four-year-old girl have died from suspected stab wounds, police said today.
The children were found seriously injured at a home on Park Lane, Carshalton, south London, last night and died later.
A six-month-old baby girl is in a critical condition in hospital.
Police have arrested a 35-year-old woman and a 39-year-old man.
A spokesman for the Metropolitan Police said officers were called at 10.30pm last night and found three seriously injured children.
"Police and London Ambulance attended, and found three children suffering serious injuries, believed to be stab wounds," he said.
The five-year-old boy and the four-year-old girl died within minutes of each other just before midnight.
The six-month-old baby girl is in a critical condition at a London hospital.
The spokesman added: "We believe we know the identity of the deceased, however we await formal identification and confirmation that all family members have been informed."
Sen Gupta, who lives opposite the couple, said they were from the Tamil area of Sri Lanka.