After the officer explained the dangers of allowing a 9-year-old to drive a car, the mum was given a warning.
Earlier in the day, Waitemata police Sergeant Brett Campbell-Howard was patrolling Beach Haven when he noticed an SUV with a 6-metre trampoline that was only loosely tied on by a thin hessian rope.
The trampoline was hanging about 1.5m over each side of the car, which was travelling about 20 km/h.
"If he'd been going any faster the tramp would have fallen off," Campbell-Howard said.
"The driver said he was moving house and the new home was only 640 metres away, he said it was too much trouble to take the trampoline apart when he wasn't going that far.
"After I explained that the fine for an insecure load was $600 and that the trampoline could have easily come off in a gust of wind and hit a car or pedestrian, the driver agreed that his method of moving it was probably not the best way."
The driver then unloaded the trampoline and made other arrangements to transport it.
"These are two events within only a few hours of each that could have ended disastrously," Campbell-Howard said.
"We know that accidents happen but so many are preventable, and going to fatalities or serious injury cases where it's obvious that the situation could have easily been prevented are the most frustrating jobs for emergency services."
He urged motorists on a public road that were being used by other motorist to think about what could go wrong before doing something risky.