Toronto police were called to an address in Scarborough were the the air con unit was found to have fallen from the eighth floor of a nearby apartment block.
The young girl was rushed to hospital but sadly didn't survive.
It's understood that the mum had just picked up her other children from school when the tragedy unfolded.
A nearby resident Sherene Bromfield described the moment she realised something was wrong when she heard the devastated mother screaming.
'I could see her trying to revive her daughter and I didn't even grab my jacket, I grabbed my keys and ran downstairs,' she recalled.
Toronto Mayor John Tory has called the incident a 'terrible tragedy.
It follows reports that after thorough investigations, no criminal charges will be laid in relation to accident.