The condition of a three-year-old girl critically injured in a collision at a London Costco last month has been upgraded to good from fair.

Police say Miah Bozek's mother, Danah Bozek-McKinnon, remains in good condition.

A newborn, named Rhiannon, who delivered by emergency C-section hours after the crash died in hospital last Friday night.

Her six-year-old sister Addison Hall died two days after the collision.

Police say no decision has been made on whether charges will be laid.