A one-year-old boy has died and a girl of the same age is in a critical condition after they were seriously injured in an "incident", according to police.
Officers were called to two children injured in a flat in Wilberforce Road near Finsbury Park in north London at 11.10pm on Saturday, Scotland Yard said.
Both toddlers had critical injuries and were taken to an east London hospital where the boy died in the early hours of Sunday morning.
The girl remains in a critical condition.
The Metropolitan Police said: "Next of kin are aware. Formal identification awaits and a post-mortem examination will be scheduled in due course."
They added that inquiries were under way to "establish the full circumstances of the incident" and said that no arrests had been made.