Ormirian, I second you, it needs to be balanced and take into account what sort of activity the child takes (ie walks to school or not, has an after school club that does not leave time for a snack before start...)
DS3 was comming back from school at one point with all his lunch minus fruit, because "only fruit and veg were healthy" according to what he had heard in school. It took me days to be able to convince him that his body needed other foods too. In the end I found a book talking about nutrition(for children) with all the food groups and NONE was banned, eventually he started eating normally again, was probably strving by this time.
I cannot help but thinking that had he had school lunch instead, he would have got on eating nothing but fruits for God knows how long before noticed.
I must say that our school menu is really nice and varied, they really made a lot of efforts in the last few years, but I am a controle freak and needs to know what they ate and how much to "balance" if needed in the evening meal.
Expat, my DCs are twigs like yours and I had several "runs in" with a particular teacher DD1 had wo was telling her off for reatng a ceral bar saying to her "and your mum thinks it is ok does she, to give you something fat and sugary?" I had to actually use all my selfcontrole to not throttle her (teacher) and tell her calmly "I agree with giving DCS a balanced diet but would not put them on a diet" as it is very different IMHO.