Health Minister Dr Jonathan Coleman and Prime Minister John Key have revealed 96 per cent of GP clinics in New Zealand have jumped on a scheme to offer free doctors visits to under 13-year-olds.

A Government offer to subsidise free doctors' visits to children under 13 has been taken up by 96 per cent of GP practices throughout New Zealand.

Health Minister Jonathan Coleman said the rate had far exceeded expectations.

"Of the 1012 general practices in the country, 96 per cent have opted in for free medical appointment, covering 98 per cent of children aged under 13."

That included rural practices too.

"It's going to make a real difference, because families aren't going to have to think twice about going to see the doctor," he said.

The Government announced the $90 million programme as part of last year's Budget, making children under the age of 13 eligible for free general practice visits and prescriptions from July 1.

But it was up to GP practices to opt in to the scheme, with the Government unable to force uptake.

A further $27.5 million over three years would mean at least 95 per cent of children under 13 would get free accident-related visits, irrespective of whether a practice had opted in.

Around 44 practices had decided not to offer free visits, many in Auckland.

It's an expansion of the scheme which until today was only offered to children under six.

"There's a proportion of those [GPs not opting in] who don't actually see children that often because the doctor's coming towards retirement and basically scaling down their practice.

"There are others for whom they feel they don't need to opt into this scheme - in the end they are private businesses," Coleman said.

In all areas where a practice had not opted in, there were other easily accessible alternatives, he said.

Currently 98 per cent of general practices offer free doctors' visits for children under six. Initial uptake for that programme was 70 per cent in January 2008, and had steadily increased to current levels.

"The main thing the Government's trying to do is give parents confidence - confidence to take their child to the doctor without being concerned about how to pay the bill," Prime Minister John Key said.

"If we can do that, then we know that youngsters will be treated earlier and the probability of there being more serious illnesses is reduced, and that's a really good thing."

He said Northland, which had applied the scheme nine months ago, had seen a reduction of children aged six to 12 in emergency waiting rooms over that time.

The "zero fees" scheme applied to a standard daytime visit to a GP or nurse at the child's regular practice where they are enrolled, and the removal of the $5-per-item dispensing co-payment.

It also covered after-hours visits to a participating practice or pharmacy.

District Health Boards were required to ensure under 13-year-olds have free access to after-hours care and prescription medicines.

For the Retimanu family, the scheme would be a "nice help".

Paul Retimanu and wife have seven children, three of which were under the age of 13.

"I think it's fantastic, it's a great initiative for parents to know they don't have to pay for it anymore."

Retimanu said if his children needed to go to the doctor, then they would be taken without thinking. But the costs did add up.

"I do know that there is a lot of families that do have to think about it. Particularly Maori and Pasifika - for our people it is difficult.

"But $40-$50 per child, we have three and times that by two visits throughout the winter period - for us that's a $300 saving."

The family had been enrolled at Wellington's Karori Medical Centre for a number of years.

The practice's owner, Dr Jeff Lowe, said the scheme would be a significant help to a large number of the 14,000 patients enrolled there.

"One in ten of those patients is in the age group 6-12 - that means just over 1400 children will get free access to the advice and treatment that they need, and the medication they need."

But Green Party co-leader Metiria Turei said there concerns the coverage only reached 90 per cent of children.

"The Government is still budgeting for one in every 10 children to still pay, we don't think that that's good enough.

"If there are going to be free doctor's visits for all children under 13, then it needs to be available to all kids under 13."

Labour's health spokeswoman Annette King said it was a good policy, and the level of uptake was "fantastic".

"I gather there's something like 40 practices that haven't joined up, and obviously the Ministry of Health will be working to get them joined up as well."

But she said there may be a negative impact on the delivery after-hours care.

"Whether they're going to be funded enough... we'll see in the next year."