Jeffery died from complications of chronic starvation on Nov. 30, 2002, in his grandparents' home in Toronto. Elva Bottineau and Norman Kidman were convicted of second-degree murder in 2006.
An inquest was scheduled to begin April 8, but will now start on Sept. 9, said Dr. Bert Lauwers, the deputy chief coroner for inquests.
The inquest will examine the events surrounding Jeffery's death, and make recommendations aimed at preventing similar deaths.
At Kidman and Bottineau's trial, the jury heard that Jeffery weighed just 21 pounds and had sores all over his body when he succumbed to septic shock from malnutrition and bacterial pneumonia in 2002.
The jury heard that his grandparents had kept Jeffery locked in a bedroom, where he lived in his own feces and was left to drink from a toilet.
Kidman and Bottineau were sentenced to life in prison with no parole for 22 and 20 years, respectively.
Last year, the Supreme Court of Canada rejected Bottineau's application to appeal her murder conviction in the death of her grandson.