The family were among seven people injured in the crash outside The Friary Centre in Guildford on Friday morning.
A boy, aged two, and his one-year-old sister were both released from hospital over the weekend, Surrey Police said.
The condition is not known of three other women who were hurt. Their injuries had been described as minor.
A spokeswoman for the force said the police investigation was ongoing.
At the time, police said the Volkswagen Polo was being driven by a woman in her 80s, and she had a male passenger with her.
The siblings were in a children's push-along shopping trolley, in the shape of a car, which was being pushed by their grandparents.
A specialist crash investigation unit has been investing the circumstances of the crash in North Street.
The grandparents of two children hurt when a car mounted a pavement and hit a group of pedestrians are still in hospital with serious injuries.