County Prosecutor Edward DeFazio said there were no obvious bruises or signs of abuse on the boy's body, but officials in his office were trying to determine if his 21-year-old mother waited too long before calling for help.
DeFazio said the death is currently considered suspicious, but not a homicide.
The child began struggling to breath while inside his mother's Bergen Avenue apartment on Saturday morning. DeFazio said the woman - whose name was not released - called 911 at about 1 p.m.
An autopsy was to be performed Sunday.