O'Brien said it was distressing that an innocent member of the community was caught up in the chase.
"She was taken to North Shore Hospital and thankfully both she and her unborn child are okay," he said.
"This has understandably caused a lot of stress to her and her family."
O'Brien said police are supporting the victim and her family and he, with the Waitemata District Commander, have visited them in hospital.
Two teenage offenders were apprehended shortly after the crash at 2.18pm.
The 11-year-old was returned home and referred to Youth Aid, and the 14-year-old appeared in the Youth Court today on charges of unlawfully taking a motor vehicle, reckless driving causing injury, burglary, escaping custody and failing to stop.
A criminal investigation and an internal investigation have been launched.
The Independent Police Conduct Authority has also been notified.
"We will be making every effort to examine our own actions to ensure we followed our fleeing driver policy and to see what, if anything, we could have done to prevent this," O'Brien said.
"he last thing we ever want is for a member of the public to get injured while police are trying to stop a fleeing driver."
O'Brien said parents and caregivers play a major role in ensuring that teenagers and children aren't driving stolen vehicles.
"Police cannot arrest our way out of this problem but we also cannot solve this issue alone," he said.
"We work closely with our partners, including Oranga Tamariki, but ultimately parenting begins at home."