Once out of the water, the relatives began performing CPR on 11-year-old Jahzel, who was unconscious.
Surf lifesavers and paramedics arrived at the scene within minutes and took over for half an hour, but were unable to resuscitate him. Police said the 7-year-old was "safe and well".
"Any drowning or any deceased victim is always very difficult to deal with, but when you have children involved it's very tough, not only on the bystanders and family members, but the lifeguards as well," said Mr Butt.
At any river mouth near the ocean, there would be a strong rip which led out to sea. "They are a place of danger ... you'll never see the flags sitting at a river mouth because obviously it is quite a dangerous place and there are often strong currents leading out from there."
Northland Emergency Services Trust rescue helicopter chief pilot Pete Turnbull said they arrived at the scene minutes after they were alerted, as they were diverted from the search for an aircraft that turned out to fine.
Mr Turnbull said the group was isolated on a bank near the Waipu River mouth, near Ruakaka Beach.
"The beach was sparsely populated - it's a very long beach and there were just wee pockets of people every 200 to 400 metres, otherwise you were pretty much on your own. The tide was half out so it was just a big isolated beach."
A man who owned a home near the river mouth said the area could be difficult for people who weren't familiar with the swimming conditions.
"I think what's happening is people are coming on holiday and it looks very beautiful and peaceful, but there are very strong currents," said the man. "There's the river mouth and the tide going out - people who are not used to the water underestimate it.
"The conditions were good, it was calm ... but the river is powerful and at 2pm the river would have been roaring out."
Another nearby resident had similar concerns about the river mouth. "The beach changes a lot. You may have gotten away with it last year - crossing or swimming - but it seems completely changed. The bar's changed, the sand's changed," she said.
The boy's death comes after nine people died in the water over the Christmas-New Year period - a "gut-wrenching" increase of four on last year's holiday toll, according to water safety advocates.
Water Safety New Zealand said the drownings over the holiday period, which ran from 4pm on Christmas Eve to 6am yesterday, were a "huge disappointment".
Chief executive Matt Claridge said the year was off to a tragic start.
Water Safety also released its provisional drowning toll for 2014.
There were 90 deaths - a 16 per cent decrease on the 107 deaths in 2013.
Holiday water deaths
• Dec 25 - Heng Li, 25, a student, died at Uretiti Beach in Northland while setting crab pots, and Imogen Saleupolu-Mataafi, 1, drowned in a temporary pool in Manurewa.
• Dec 26 - Simon Camp, 47, died at Karioitahi Beach while surfing.
• Dec 27 - Jarod Lineses, 16, was swept out to sea on Ninety Mile Beach at Hukatere in the Far North.
• Dec 29 - Terangi "Toots" Woonton, 59, and Kairangi Samuela, 53, died when their 5m vessel was swamped crossing the Manukau Bar.
• Jan 1 - Kris Wichman, 36, drowned in the Patea River after rescuing his niece and two daughters.
• Jan 1 - Wayne August, 42, was seen by beachgoers walking into the surf at New Brighton beach in Christ-church wearing long pants and a T-shirt.
• Jan 4 - The police dive squad recovered the body of a Far North man who went missing near Hihi Beach on his boat on Saturday. Police believe there were no suspicious circumstances.
