Police said in a statement the actions were dangerous and could have led to a serious accident.
"Wearing your seatbelt and making sure your children are properly restrained will keep you and your children safe, as even a low-speed impact can cause to a great deal of harm to an unrestrained child," a spokesperson said.
"Keeping children restrained at all times when they are travelling in a vehicle also reduces the risk of the driver getting distracted, which could potentially pose a risk to the safety of other road users."
This is not the first time a child has been spotted driving a car in Auckland.
At the beginning of this year, a motorist shared her disbelief after witnessing a preschooler steering a car on Auckland's Southern Motorway in peak hour traffic.