Nearly every general practice is expected to sign up to the Government's new zero fees for under-13s regime, though some say they cannot rule out raising the cost of adult consultations to cover their costs.
The policy was widely praised by health professionals, though doctors said its true value would not be apparent until the level of state subsidy was confirmed.
The Rural General Practice Network, which represents 200 rural GP clinics, said incomes at these practices took a hit when free visits and prescriptions were introduced for children under 6 because funding did not completely cover the cost of the appointments.
Chairman Dr Jo Scott-Jones said: "We're really enthusiastic about the idea of providing care that's free at the point of contact, it makes a lot of sense. But it needs to be done in a way that's sustainable for the businesses."