GPs are free to continue charging parents private fees for children under six despite the Government's free-care scheme being introduced this summer.
There is no legal ban on doctors asking for regular private fees of around €60 a visit if they decide not to sign up to the state contract on free GP care.
The new scheme would extend free GP visits to around 240,000 under sixes whose parents currently pay for their care.
But Dr William Behan, a GP in Walkinstown, Co Dublin, predicted that less than 10pc of family doctors will sign up to participate.
Dr Behan, who has studied visiting patterns and costs in general practice, was among 200 doctors who attended an angry 'Weathering the Storm' special meeting of the Irish College of General Practitioners (ICGP) in Clonmel, where Junior Health Minister Alex White was jeered.
Dr Behan said parents who currently take their child to the doctor an average of three times a year are likely to double that number of visits if the service is free. He also expects many of these visits would be in the evening and night.
"The visits would mostly be about head colds and coughs," he added. There are around 420,000 under sixes in the population and 180,000 of these already have free care through a medical card or GP visit card.
Most GP practices could not cope with the extra workload it would involve, including a compulsory annual health check for every child under six on their books, Dr Behan said.
"There is no evidence to show this check of height and weight would be of benefit," he stressed.
The conference heard it would be the wrong use of scarce resources for GPs, who have already seen their state fees under the medical card scheme cut.
"It's not about money – it's about the loss of control of your own practice," he added. GPs are expected to get around €75 a year for each child.
Dr Darach O Ciardha, spokesman for the ICGP, warned that family doctors are now galvanised against the draft contract for free care, and said that the under-sixes plan is "ill-conceived".
Some GPs told the conference that several of their patients believe the under-sixes free care scheme is already in place and they are asking not to have to pay a fee.
Earlier, psychiatrist Prof Jim Lucey of St Patrick's Hospital told the doctors "recession depression" is now common among medics.
"Panic anxiety, avoidance and addiction are increasingly prevalent. But the average delay between onset of symptoms and professional help is 10 years, the resilience of those in primary care is threatened.
"Don't wait any longer to be happy," Prof Lucey urged the doctors. "We can't wait any longer to lead mentally healthy lives."