Emergency services were called to a house on Bosworth Road, Adwick, Doncaster, at about 11am yesterday (Wednesday January 8) following reports from the ambulance service that the boy was in cardiac arrest.
He was taken to hospital where he sadly died this afternoon (Thursday January 9).
A post-mortem examination is expected to take place later this evening.
A 36-year-old man and a 32-year-old woman, both from Adwick, have been arrested on suspicion of murder and are currently in police custody for questioning by detectives.
Detective Chief Inspector James Axe, the senior investigating officer, said: "The loss of any life is tragic, and the death of this little boy is undeniably devastating.
"Our thoughts are with those who are affected and our specialist officers will continue to support them.
"We have a dedicated team of officers assigned to this investigation. Two people are in custody and we are working hard to establish the exact circumstances leading up to this child's death."
T/Detective Chief Inspector Anna Sedgwick, from Doncaster, said: "I know a case such as this will have an impact both within the local community and more widely. We will have officers in the area today and encourage anyone who has any concerns, or would like to speak to someone, to approach a member of our team.
"I would also please ask that people are mindful of what they post on social media, particularly in relation to any speculative comments, and keep in mind the impact this could have on the boy's loved ones during this incredibly difficult and traumatic time."
Anyone with concerns or information is asked to call police on 101 quoting incident number 293 of 8 January 2020.