I agree but it's also naive to say that we should allow parents to give their children anything they want because some simply are ignorant to the fact that high fat/sugar foods are not good for anyone is large quantities. As most things, there is a middle ground which I think is probably the best approach.
The only intervention a school should do is to educate the child and pass information onto the Parent via the child if it is necessary...it should not dictate responsibility.
Anything else should be up to qualified and experienced professionals in the field relevant to the concern.