"I would say 80 per cent of that is about what they are eating.
"Children are eating too many inappropriate, processed, packaged foods - which are high in fat, salt and sugar - and less fresh food. These foods are also less filling so they eat more of them.
"Their diets have moved away from the simple meat, veges, fruit and bread.''
Mrs Scrivin said parents had to take responsibility.
"It does require effort from the parents and the amount of effort they're prepared to put in reflects back on their children. Parents have a moral responsibility to make sure they are nourished properly.''
She said schools also had a role to play in monitoring what pupils were eating. Children regularly presenting with inadequate or inappropriate meals should have notes sent home re-emphasising the health message.
Exercise was fundamental to tackling the problem, said Mrs Scrivin. "The Ministry of Health recommends one hour of exercise a day but there are plenty that don't do that. And we're not just talking about kicking a ball about. It should be running around, exercise which makes you breathe hard.''
Exercise need not be expensive, she said. "People will tell you it's expensive but it doesn't have to cost much, or anything. You can go for a run on the beach or in the park. Get a dog - they need exercising every day.''
Mrs Scrivin's comments come as researchers from the University of Auckland announced study results showing excessive weight and obesity in New Zealand costs the country between $722 million and $849 million a year in healthcare costs and lost productivity.
Ministry of Health statistics state one in five children, aged 2 to 14, in New Zealand is overweight (20.9 per cent). A further one in 12 is obese (8.3 per cent) and the health of three in 10 children (29.2 per cent) is at risk because of excessive weight.
New Zealand was ranked 29th of 30 countries in the Organisation for Economic Co-operation and Development (OECD) 2009 report Doing Better for Children for child health and safety.
Joe Bourne, who works as a GP liaison for the Bay of Plenty District Health Board, said obesity in children was having serious consequences.
"The most significant change I am noticing is the increasing numbers of teenagers presenting with Type 2 diabetes. Type 2 diabetes was previously known as maturity onset diabetes but the age at onset is coming down.
"Type 2 diabetes has multiple risk factors, including family history and ethnicity, but is also associated with obesity. Type 2 diabetes that develops in young people can be particularly challenging to manage and as such there is an increased risk of complications such as kidney and eye damage.''
The organisers of last week's The Big New Zealand Play Hour further revealed children's activity levels had fallen by a third in less than a century.
