Unison is demanding a national agreement

The action by Unison members follows a series of one and two-day walkouts over the past 10 months.

Local deals have been struck with staff in eight council areas, but Unison has repeated its call for a national agreement.

Unison estimated that 4,000 people are taking part in the all-out strike.

Eight of Scotland's 32 councils have reached local settlements and umbrella body Cosla said that was the "only way" to resolve the dispute.

LOCAL SETTLEMENTS Aberdeen East Renfrewshire Falkirk Highland Perth Shetland South Lanarkshire Stirling

Cosla president Councillor Pat Watters said the indefinite strike was "absolutely unnecessary".

He said: "We still believe there is room for negotiation at local level, eight authorities out of 32 have settled at local level.

"An all-out strike is absolutely unnecessary, because the other authorities are ready, willing and able to settle this strike if Unison locally will sit down and talk to them.

"We would urge to people to do that. To sit down locally and get a resolution to this dispute and stop putting children through this torment of not being able to get to nursery."

Joe Di Paola, Unison's Scottish organiser, said the dispute would shape the future of the nursery service.

The employers have admitted that the route to a settlement lies through a Scotland-wide regrading Joe Di Paola Unison's Scottish organiser

"The employers have admitted that the route to a settlement in this dispute lies through a Scotland-wide regrading," he said.

"Yet they refuse to take these steps, preferring to force nursery nurses out on strike than deal fairly with their claim."

Carol Ball, chair of Unison's nursery nurses working party, said her members were subject to national standards and any pay agreement should also be implemented nationally.

She told BBC Radio Scotland: "Our job is the same across the country. It is determined by national standards, by the national curriculum documents - early literacy, early numeracy - these are all determined by the Scottish Executive.

Nursey nurses claim they are underpaid and undervalued

"We've got the same qualification across the country, so therefore we maintain that we do the same job, so we don't want local settlements.

"What we don't want to see is nursery nurses being paid different rates across the country, because then it's a postcode lottery. It's a nonsense, we should be paid a national grade."

Pay ceiling

A 23-year-old nursery nurse on the picket line said she was on strike because she would reach her maximum wage of �13,800 in April, with no prospect of another increase.

Unison predicted that 90% of nursery nurses are taking part in the all-out strike starting on Monday, which was called after a ballot of union members.

Nursery nurses earn about �13,000 a year, but want an increase of �4,000 to reflect the extra duties they have had to undertake.

The union has rejected Cosla's offer of a new grading system which would enable fully qualified nurses to earn �18,000.