A couple have been arrested on suspicion of murdering a one-year-old boy they were set to adopt.
Police said a 37-year-old woman and 34-year-old man, from Barrow-in-Furness, had been arrested on suspicion of murder, causing or allowing the death of a child and two counts of assault.
They have been released on bail, Cumbria Police said.
Cumbria County Council said the child was under its care but was living with the couple before the adoption.
The council said it had recommended an independent safeguarding review was carried out.
Police said the North West Ambulance Service (NWAS) was called on 6 January and the child was taken to Furness General Hospital in Barrow before being transferred to Alder Hey Children's Hospital in Liverpool.
He died the next day.
Det Ch Supt Dean Holden said: "Two people have been arrested as part of an ongoing investigation into the tragic death of a one-year-old boy in Barrow.
"An investigation is under way by a dedicated team of detectives and other specialists in order to establish the full circumstances of the death in full consultation with the coroner."
The county council said a final adoption order had not yet been granted by the courts, however it is a requirement of the Adoption and Children Act 2002 that a child lives with their adoptive parents for a period before an application for an adoption order can be made.