There has long been a tradition in Wales of sending children to school at a particularly early age, especially in rural areas. And LEAs stress that all the classes have a nursery assistant as well as a teacher.
However, Hywel Jones, director of Mudiad Ysgolion Meithrin (the Association of Welsh Medium Nursery Groups and Playgroups), said: "Wales has always been in the vanguard of nursery education and we are in danger of losing that advantage."
He claims there is not enough co-operation between LEAs and nursery groups to save playgroups from closure.
Almost all the Welsh authorities are opposed to the nursery voucher scheme, but many have accelerated policies on admitting three-year-olds to school because of the need to claw back the money the Government has taken off them for vouchers.
Five years ago, Gwynedd introduced part-time education for three-year-olds in 17 schools, and now Anglesey, a new authority that was formerly part of Gwynedd, is extending the policy to a further 18 schools.
Geraint Elis, Anglesey's assistant director of education, said: "I am not an expert in early years education at all. I certainly have my concerns about children starting school early, but people are very anxious that the earlier you get them the better.
"In the past they did attend voluntary nursery provision. They are not taught reception or Year 1 curriculum. They are in a nursery group but under the eye of the key stage 1 teacher."
Many of the classes with three-year-olds had received "glowing" reports from the Office for Standards in Education, he added.
In Gwynedd, director of education and culture Dafydd Whittal, says it has always been the authority's policy to integrate playgroups into schools.
The authority considered three options: to continue admitting children to school after their fourth birthday and lose up to two terms of vouchers; to admit children three times a year; and to offer 12 months' part-time education from the age of three.
Mr Elis said: "If we had kept the status quo, we could have lost two terms of vouchers. It would have meant a loss of money to the whole system. Therefore we had no choice but to change the policy."
Gwynedd has employed an additional adviser for two terms to ensure that three- and four-year-olds in small schools receive the right education.
The charity, Children in Wales, is concerned that in many rural areas some three-year-olds begin school full-time.
In a paper on early childhood services and vouchers for the Department for Education in 1994, it said: "Many teachers expressed feelings of immense frustration and isolation when they failed to balance the conflicting curricular and emotional needs and demands of the wide age-range of children in their classes, often from three to seven years."