High charges raise concerns that parents may not take sick youngsters to see the doctor.
It is cheaper to take a 10-year-old to the doctor at many clinics in upper North Island regional areas than in Auckland.
About 40 clinics in Auckland charge $40 or more for a standard medical consultation during office hours for an enrolled child in that age group. The highest advertised fees are $50 to $60, although the clinic listed at $60 says it actually charges $40.
In the Waikato health district, the highest listed fee is $30, at Whitianga. For the Rotorua-Taupo area, the top fee is $27 at two clinics, for teens aged 13 to 17.
Parents in the Bay of Plenty health district are generally forking out more than in the other provincial areas: 12 clinics charge $30 or more for children 6 to 17, with a top listed fee of $39.50.
Keriana Brooking, the acting chief executive of the Midlands Health Network - a Hamilton-based organisation linked to 91 practices serving more than 400,000 patients from Gisborne to Taranaki - said the varying prices of land in different suburbs was one of the factors accounting for the wide range of fees.
"General practices reserve the right to charge a reasonable fee within their geographic area based on age," she said. Staff pay rates could also vary depending on employment agreements, "and sometimes it's whether or not people invest in more up-to-date equipment. That's not saying the older equipment isn't fit for purpose".
She said it wasn't possible to say if higher fees meant longer consultations, because the length of visits varied greatly depending on the needs of the patient and other factors such as the time of year.
A leading primary care researcher, Professor Jackie Cumming, of Victoria University, is concerned by some of the higher fees charged by GPs for children 6 and older.
"We do know that if the fees are too high, people won't use their GP services," she said. "There is some evidence they will use more hospital emergency department services. There's international evidence that shows people will be sicker if they are not using primary health care services."
Professor Cumming said the 1999-2008 Labour-led Government focused on increasing primary care funding - in part to reduce fees - and on creating primary health organisations, but didn't do enough to integrate primary and hospital care.
National had reversed that. Hospitals were devolving some services to primary care and integrated family health centres were being set up, with a wider range of health practitioners, but funding problems had emerged.
"We should be putting more money into keeping those fees low if we really do want people to access primary health care services."
She suggested a fees exemption for the rest of a year once families reached 20 GP visits, similar to the scheme for the $5 pharmacy prescription charge. However, she said the prescription charge system was flawed: the fees were often not waived when a person was entitled to this.
Health Minister Tony Ryall said National had done a great deal of work on integrating services and had put a lot more money into primary health care.
"We've increased funding for primary care subsidies by over $180 million compared to 2007/08. Funding for the very low-cost access scheme has increased by more than 65 per cent from $27 million in 2007/8 to $45 million this financial year.
"We are putting in an extra $12.8 million for more patients to access CarePlus, a general practice programme providing additional support for patients with long-term conditions such as diabetes and asthma."
His spokeswoman said people who visited their doctor 12 or more times a year were entitled to discounts on some health services.
The Health Ministry says these include extra subsidies for after-hours visits, and for seeing a doctor who is not the person's regular GP.
Factors that influence general practitioners' charges
* The bottom line: general practices are free to set their own fees like any business.
* Most receive state bulk funding and can be required to justify fee rises above a "reasonable'' level.
* Extra state money is given to clinics which agree to cap fees at zero for under-6s, $11.50 for 6- to 17-year-olds and $17.50 for those 18 or older.
* That scheme is now restricted to clinics with a population of at least 50 per cent Maori, Pacific and low-income people.
* Clinics not in that scheme can also get extra funding if they agree to free under-6 visits.
Note: Applies to medical consultations during office hours for enrolled patients.