The children have been taken to hospital.
Staff at the school the girls attend are in shock after the crash.
"They are really lovely, sweet girls," said a View Road School administration worker.
"They were following the road rules.
"We're all in shock and just glad it wasn't worse.
"It's bad enough as it was but we're thankful they weren't killed."
School principal Chris Hull raced to comfort the injured sisters as soon as she heard about the crash.
"She told me one of the girls was in extreme pain," the school worker said.
The girls' grandmother was also believed to be walking with them when they were hit.
Police say family members are with the girls in hospital.
A 30-year-old Waiuku man has been charged with two counts of dangerous driving causing injury.