Little Reuben McNulty was left fighting for his life following the attack at a home in Yaxley, Cambridgeshire, in the early hours of 18 November.
Two Staffordshire bull terriers removed from the address at the time have been destroyed, police said.
The couple who live at the house are believed to be Daniel McNulty and his partner Amy Litchfield.
Following the incident, a man at the property who did not want to be identified, said: "They're in bits, they're devastated."
Reuben was initially taken to Peterborough City Hospital with life-threatening head injuries before being transferred to Addenbrooke's.
Police said a 28-year-old woman and a 31-year-old man, both from Yaxley, arrested on suspicion of child neglect have been released under investigation.
Officers said the death was not being treated as suspicious and the case has been handed to the coroner.