Firefighters were called to help on Saturday after a mother accidentally locked her 9-month-old child in a car.
Whanganui Fire station officer Shane Dudley said the crew were called to the post shop about 11.40am to help free the baby from the car.
"The 9-month-old was sitting back, smiling away," he said.
They were able to use a coat hanger to open the car door.
If the baby had been in distress, they would have used a faster method, Mr Dudley said.
"We chose to take our time and use a little bit more finesse."