Safety concerns have forced kitchens at more than 30 Derby schools to be closed.
The city council said it had to temporarily close down 33 kitchens on Monday because of possible problems with gas appliances.
Some schools are taking meals from other working kitchens but thousands of children are being given sandwiches and fruit instead.
Officials said it could be up to three weeks before all problems are resolved.
Jo Davidson, strategic director for children and young people at the council, explained action was taken after inspectors flagged up a potential issue with some appliances.
She added: "If there are concerns about gas safety it's not something you can hang around with.
"So although it is regrettable it happened at short notice, equally we have to be sure that children and staff are safe."
Full checks should be completed by 16 November but parents are being asked to plan for disruption for up to three weeks.