When a young mother left her unit to buy groceries in NSW's Hunter Valley in 2005, she had no idea she would never see her 21-month-old son Jordan Thompson alive again.

Bernice Swales returned to find her child naked on a bed, with her then-boyfriend Cecil Kennedy attempting CPR.

Jordan Thompson died after ingesting a lethal overdose of antidepressant medication.

She picked up Jordan and ran across the road to Singleton Hospital, stumbling and falling onto her elbows at times as his eyes "started to go to the back of his head", but he had no brain activity and was pronounced dead.

Mr Kennedy told police he left the toddler playing in the bath for 40 to 90 seconds and returned to find him face down.