All children in the first three years of school should be entitled to a free, healthy lunch, a group of unions, churches and children's organisations has said.

In a letter to First Minister Alex Salmond the group, including charity Children 1st and the Educational Institute of Scotland, said prioritising investment in meals for primary one to three pupils would provide a "well evidenced, direct and immediate boost to the wellbeing of children and families across Scotland".

Earlier this year, Deputy Prime Minister Nick Clegg announced children in the first three years of schools in England will get a free lunch from September 2014.

The Scottish Government made a similar pledge in 2010 but progress has been "limited", according to the 11 organisations who have signed the letter.

They are now calling for money from Barnett consequentials, which boost the Scottish budget in line with Westminster spending decisions, to be used to provide free school lunches.

The signatories to the letter, who also include Shelter Scotland, Unison and the Poverty Alliance, go on to say that "a universal approach in the early years has been demonstrated to have a positive impact on the take up of healthy school lunches, on children's readiness to learn, and on supporting home life".

John Dickie, head of the Child Poverty Action Group in Scotland, said: "The Scottish Government has led the way in piloting universal free school lunches. The Autumn Statement now provides the financial details Scottish Ministers said they needed before delivering on their commitment."