Leslie McDonald, 51, was arrested by Halton homicide detectives. She has been charged with criminal negligence causing death and failing to provide the necessities of life after an autopsy was performed on Maximus Huyskens, 2, who died on a sweltering afternoon late last month.
Police had said the boy was left "for an extended period of time" inside a sedan parked outside his parents' Milton townhouse. He had earlier been left in the care of his grandmother while his father was at work and his mother was at an appointment.
McDonald is scheduled to appear in Milton Court on Aug. 14.
The Canada Safety Council estimates that between four and six children die from being left unattended in vehicles every year. During a summer day, internal temperatures can rise to 50 C in as little as 10 minutes.