A police spokeswoman said the girl told police she had run onto the road without looking, and no charges would be laid against the driver.
According to the witness, the driver was visibly shaken after the crash and was consoled by friends, also dressed in onesies.
St John spokesman Robbie Walker said they received a call at 8.32am, and one 16-year-old patient was taken to East Care medical centre with moderate injuries.
Macleans College deputy principal Jim Lonergan said he was not aware of any of the school's students being involved in the accident, however he said there was a mufti day at the school today.