A DHB spokeswoman said the mother was "quite unwell" when she was brought into the hospital yesterday, but was now in a stable condition.
Whangarei Senior Station Officer Brad Cunningham said as they began to free the woman they realised she was covering the young girl.
"She was entangled in the display case. We cleared a bit of the debris away and found the girl under her," he said.
The woman could not stand up and firefighters placed her on a stretcher and she was transferred to an ambulance.
"It wasn't a very nice scene when we turned up."
The little girl and the elderly man were discharged yesterday, said the DHB spokeswoman.
The shop's owner, Jenny Gu, said: "It's terrible. It hit a lady and her kid. They were just standing beside the case waiting for service and the car crashed into them.
"The customer had just told my staff member what cake she wanted and my staff and gone into the back to get it out when the car crashed. It was for the little girl's birthday. It is so terrible."
St John spokesman Robbie Walker said the girl suffered moderate injuries and the elderly motorist was initially assessed as having minor injuries but was later upgraded and also transported to hospital.
"Multiple other patients" were treated at the scene for minor injuries.
Mrs Gu said there was extensive damage to the store, with broken glass and damaged furniture throughout.
"The whole shop is very damaged. It has damaged the whole shop front, the whole show case is broken and there is glass everywhere. The tables and chairs are damaged."
- Additional reporting Kristin Edge of the Northern Advocate