Australians need to reset their understanding of what is a normal weight, with more than one-in-five school aged children in New South Wales now considered overweight or obese, health experts say.

New data indicates there is a disconnect within society about what is now considered a 'normal' weight, said Kerry Chant, chief health officer at NSW Health.

"GPs have told us that sometimes it's actually hard for them to raise healthy weight with families," Dr Chant said.

"That's partly because 70 per cent of parents of children who are overweight think their child is about the right weight, so the GPs said to us, we need some more help with some practical tools."

New tools to address the growing childhood obesity epidemic have been launched including a website showing a healthy weight calculator and a video of a nutritionist giving a guided tour in a supermarket to highlight better food choices.

Dr Chant said new and clear ways have to be found to reach families.

"As a society we've got fatter. So we've got over 50 per cent of adults are overweight or obese," she said.

"And sadly one in five children are above a healthy weight in NSW, so you can imagine that the norms of healthy weight have actually changed."

Obesity treatment must be equitable

Australian Medical Association spokesman Brad Frankum said the most insidious problem with the obesity crisis is that it is unevenly distributed.

"Western Sydney and the Nepean Blue Mountains are in the top three metropolitan areas in Australia when it comes to overweight and obesity rates so we need to do everything we can to ensure that access to prevention and treatment is equitable," Professor Frankum said.

"I don't quote these figures to fat shame or judge people in the community where I work. We're just talking about the most significant health issue that Australia is facing."

Professor Frankum said it was important to normalise healthy eating early on, because research showed more than 80 per cent of children who were obese become obese adults.

"There does seem to be an element of metabolic setting that happens in childhood that once you reach puberty— if you're overweight, it does become harder to lose weight beyond that, so it is something to do with the way the body gets used to the nutrients that it gets."

Dr Chant said the new tools would help parents to recognise when their children were overweight.

"They may take it as a judgement, they may take it as blame, and so to better support general practice we need to develop tools to normalise and promote the conversation," she said.