The $90 million programme was announced as part of last year's Budget.
Previously, free visits were only offered to children under 6.
Those that have signed up to the expanded scheme include Richmond Road Medical Centre.
In April, the Herald reported the Grey Lynn practice was one of only 11 in the country that had not signed up for the scheme for under 6s.
At the time, Dr James Beetham criticised the use of the word "free" as propaganda and a vote-buying tactic.
Yesterday, he said the practice had reluctantly signed up and there was no charge for children under 13.
He said families had not minded paying the $18 fee, because of the quality of service provided.
"We have got to the stage now where we feel we just have to not charge for under 13s ... actually in the short-term we will be better off if we don't charge," said Dr Beetham.
"But one of the problems is medical inflation is going up significantly faster than general inflation.
"So probably in two to three years' time, we will be losing money hand over fist," he said.
Of the 34 practices in wider Auckland not involved, nine had indicated they would join shortly.