Surf Life Saving Northern Region (SLSNR) is urging parents to look after their children while at the beach after a number of kids needed to be rescued while swimming on Wednesday.
Surging waves on the west coast of Auckland saw lifeguards at Bethells Beach assist 31 people to safety - including children - most of whom had lost their footing and were almost swept away in the strong current.
"It's simply not enough to watch from the shore, especially given the surging conditions seen on the west coast yesterday," SLSNR Chief Executive Officer Matt Williams said.
"Please don't overestimate your ability or your children's ability to cope in the conditions."
Williams said children should be within an arm's reach of their parent or caregiver.
"Secondly, always swim between the flags, and educate your children about the importance of swimming between the flags. It's up to all of us to lead by example," he says.
"We know beaches are especially dangerous with king tides and large swells, and this is already stretching lifeguard services across the country. It is all the more important for parents and caregivers to play their part."
At Waipū Cove and Ōrewa, lifeguards also had to embark on "time-consuming" searches for missing children.
Williams said parents and caregivers should be carefully supervising their children while they were on land as well.