Concern is growing about plans to extend early years sessions for three and four-year-olds from next year.
All children of that age are already entitled to 12.5 hours of free education. In most nurseries, this means five two-and-a-half-hour sessions. But from September 2010, the entitlement rises to 15 hours a week - effectively lengthening nursery sessions to three hours.
Parents will also be able to use the entitlement more flexibly, such as grouping it into three days a week.
The extension of sessions is already under way and by this September all authorities will be required to make more time available to their 25 per cent most disadvantaged youngsters.
The Department for Children, Schools and Families has published guidance for authorities on how to introduce the change and consultation is to be carried out this spring.
Christine Blower, acting general secretary of the National Union of Teachers, said: "There are already problems because authorities are beginning to work out how to provide for the 25 per cent of the most deprived children this September.
"Everywhere will have some children entitled to this extension to their nursery provision and so there will be concerns that teachers' conditions of service will be worsened. The answer is to have more nursery assistants and nursery teachers."
An evaluation of pathfinder nurseries that tried the extended flexible provision was published recently. It noted concern among schools at having to provide "childcare" and going over contractual hours. Voluntary and community sector nurseries were generally enthusiastic, but the private sector was concerned it was not financially viable. Several local authorities reported that providers had now opted out of early years.
Sheffield local authority, which began trialling the service in April 2007, initially had the co-operation of only two schools. This rose to 20 and six more were "getting there" by July 2007, when its report was published. Blackpool found that "schools are finding this agenda very challenging".
Exhausted staff, pages 32-33.