Two people have been arrested on suspicion of murder following the death of a two-year-old boy from Broadmayne, Dorset Police said.
A man and a woman, both aged 21 and from the Dorchester area, are currently assisting police with their enquiries.
Emergency services were called to an address in Broadmayne, near Dorchester, Dorset, where the toddler was seriously ill.
He was taken to Dorset County Hospital, where he was pronounced dead.
Inspector Mike Darby, of Dorchester Police, said: "I appreciate the incident has impacted on this close-knit community, but it is important we understand the full circumstances surrounding the death.
"An investigation has been launched and there may be some police presence in the village while detectives carry out their investigations.
"If anyone in the local community has concerns, they can speak to their local neighbourhood policing team who will be able to offer reassurances.
"I would also like to remind the public that certain legal constraints apply as people have been arrested in connection with this investigation.
"Therefore Dorset Police would hate for anyone to accidentally impact on the investigation by posting well-intended but inappropriate comments on social media."