A two-year-old boy died from a "blunt force trauma" to his abdomen that caused internal injuries, an initial post-mortem examination has found.
The toddler was discovered seriously hurt at a property on Arthur Street, Northampton, on Friday and was declared dead in hospital.
A final cause of death would be revealed after more tests, police said.
Raphael Kennedy, 30, has been charged with murder and will appear at Leicester Crown Court on Wednesday.
The post-mortem examination took place at Leicester Royal Infirmary.