Police have arrested a woman in her 40s on suspicion of murder after a boy was found dead at an address in Cumberland Park, Acton.
The murder investigation was launched after the boy aged 10 was found dead.
The woman was arrested after walking into a police station in the early hours of Sunday morning to speak with officers.
Scotland Yard said police believe they know the identity of the child, who was known to the woman.
No one else is being sought in connection with the death.
Detectives from Specialist Crime are investigating and a post-mortem examination will be arranged in due course.