A two-year-old girl and a four-year-old boy have gone missing from their home in north London.
Police discovered Tiffarah Paul-Wright and Aiale Paul-Wright had disappeared after officers were told the pair were home alone.
Tiffarah and Aiale were last seen at around midnight on Monday at an address in Islington, the Metropolitan Police said.
"Officers were made aware that the children were at home alone, but officers visited the address and they were not present.
"Officers are growing increasingly concerned for their welfare," the force said.
Anyone who has seen Tiffarah and Aiale or who knows where they are is urged to call Haringey Police on 101 or 999 if sighted immediately, quoting reference 17MIS054702/04."