The Northland Electricity Rescue Helicopter was able to be diverted from the gyrocopter search to the river mouth, where paramedics found relatives had managed to pull both children from the water and were performing CPR on the 11-year-old boy.
Paramedics tried to resuscitate him for another 30 minutes, but their efforts failed, pilot Pete Turnbull said. "It was a good response but not a good result." Surf Life Saving Northern Region operations support officer Chase Cahalane said lifeguards from Waipu Cove were also initially called to help in the search for the gyrocopter and were then diverted to the river mouth by police.
Lifeguards arrived to find four people on the beach, including the two children, as well as the Northland Electricity Rescue Helicopter paramedics.
"It's obviously quite a difficult situation, particularly when the patients are so young."
Water Safety New Zealand chief executive Matt Claridge said it is important for parents or caregivers to keep a close eye on children while swimming.
"One of the single most prominent reasons children drown was because of a break in supervision.
"You need to watch what they're doing, what they're up to, you can't be distracted.
"Never ever take your eye off of kids while they're swimming," added Claridge.
The drowning death is the third in the region in 12 days.
Auckland student Heng Li, 25, drowned while setting crab pots on Uretiti Beach on Christmas Day, only kilometres away from yesterday's drowning.
Jarod Lineses, 16, was swept out to sea at Northland's Ninety Mile Beach on December 27.
His body was found on New Year's Day.
Seven people drowned in New Zealand waters this official Christmas holiday period (4pm Christmas Eve until 6am yesterday morning) - two deaths more than the same period last year, which Mr Claridge described as a huge disappointment.
Meanwhile, the gyrocopter that sparked the initial emergency services call-out at around 1.15pm was located at 2.35pm at Whangarei Airport.
Ms Kennett said further inquiries revealed that it was most likely the gyrocopter had been flying up and down between the sand dunes, which could have caused the impression that it had crashed.