Every child in the first three years of primary education could receive free school meals if a pilot project is successful, ministers have said.
The trial will start when pupils return from their October holiday
A Holyrood committee has voted in favour of a £5m trial scheme.
More than 35,000 children in primaries one to three in Glasgow, the Borders, East Ayrshire, West Dunbartonshire and Fife will take part in the pilot.
However, ministers were criticised because councils had informed parents of the trial before it was approved.
The scheme is due to start in a few weeks' time.
Adam Ingram, the children's minister, said that if the six-month pilot was judged to be successful, the Scottish Government would aim to expand the scheme to all pupils in the first three years of primary school.
He also said the SNP administration hoped to extend the number of students eligible for free meals, so that more children from lower income families could benefit.
"We need to extend eligibility right across the piece and we will certainly be looking at that in the future," he said.
MSPs have been told that expanding free school meals to all primary one to three pupils could cost £30m to £46m a year.
Mr Ingram says the government is considering extending eligibility
Scottish Government official David Cowan said increasing eligibility could cost between £16m and £31m a year on top of that.
Mr Ingram said the pilot was being set up to establish if there was any change in attitude among children and their parents to healthy eating.
Statistics revealed that obesity levels in Scotland were the second highest in the developed world behind America.
The scheme was approved by members of the Education, Lifelong Learning and Culture Committee, but still has to be passed by parliament.
Committee convener Karen Whitefield said it was "a little bit premature" for letters to be issued to parents when it had not been given parliamentary approval.
She said: "It seems to be that parliament is being ridden roughshod over."
Conservative children and schools spokeswoman, Liz Smith, said: "It was a great surprise to suddenly find these letters had been issued where it makes it clear to the parents concerned that they are eligible to receive these meals."
She told the minister: "I think our judgment has been slightly compromised."
Mr Ingram admitted that "it might have been better to wait until after today's meeting" before the letters went out to parents.