Two children's charities have cast doubt on the Scottish Government's free school meals pilot programme.
Free meals will be given to children in P1 to P3 classes
They said free meals for children in the first three years of primary school may not be the best way of improving diet or tackling poverty.
The £5m, six-month pilot scheme is being trialled in five local authority areas from October.
Ministers said it was about addressing a gap between the number of children in poverty and those who get free meals.
The pilot scheme will run in the Borders, East Ayrshire, Fife, Glasgow and West Dunbartonshire to gauge its popularity among 35,000 pupils.
Representatives from Barnardo's and the Aberlour Trust told the Scottish Parliament's education committee that the pilot was too short a time to change cultural habits.
Tam Baillie, of Barnardo's, said confining free school meals just to pupils in the first three years of primary school would not help pre-school children and older children, adding that targeting help would be a better use of resources.
"We have 25% of children living in poverty in Scotland, yet only 19% qualify for free school meals," he said.
"That's a gap that has to be addressed. That will remain outstanding regardless what happens with the free school meal pilot."
However, children's charity Children in Scotland gave strong support to the pilot for P1 to P3 pupils.
Paula Evans, the charity's policy and parliamentary officer, told the committee: "It is right for Scotland to test the benefits of an inclusive free school meals policy that will encourage healthier eating habits, combat childhood obesity and improve the social development of school children at the P1-P3 level.
"We look forward to the outcomes of this pilot.
"If proven successful, then Children in Scotland hopes to see it universally expanded beyond the current six month time span to all P1 to P3s in Scotland - and indeed to young children in pre-schools."
The results of the trial will be evaluated next year and the SNP administration will then have to decide whether to roll it out across the country or whether, as the opposition parties believe, it is better to extend the eligibility for free school meals to more families living near the poverty line.