A man and woman have been arrested on suspicion of the murder of a two-year-old boy.
Merseyside Police are investigating the death of the toddler, who was found unresponsive at a house in Birkenhead, Wirral, on Wednesday afternoon.
Paramedics were called to the home on Woodville Road at about 2.30pm and carried out CPR on the child.
He was later pronounced dead at Arrowe Park Hospital.
A 28-year-old man from Birkenhead was arrested on suspicion of murder and a 24-year-old woman, also from Birkenhead, was arrested on suspicion of murder and child neglect.
Both are being questioned by detectives.
A police spokesman said: "The force has implemented the protocols for a sudden unexpected death in infancy and a detailed examination of the circumstances is being carried out."
Two other children, aged two and three, have been medically assessed and are in the care of Wirral Council's Children's Services.