A 29-year-old man and a 22-year-old woman have been arrested on suspicion of the murder of a two-year-old boy, police have said.
The child, who has not been named, was pronounced dead on Sunday night after being taken to hospital from an address in Ward End, Birmingham.
West Midlands Police said a post-mortem examination indicated the boy died as a result of "non-accidental injuries".
A spokeswoman said on Wednesday: "All of the family have now been informed and a family liaison officer has been appointed to support them during this difficult time.
"A 29-year-old man and a 22-year-old woman were arrested on suspicion of murder at the time of the incident and have been helping police with their enquiries.
"Yesterday morning officers were granted a warrant of further detention at Birmingham Magistrates' Court."
Police now have until 10.30pm to continue questioning the pair, who are understood to be the boy's mother and her partner.