This is really shit. So many things the school has done wrong here. This is the same reason many businesses have a policy that the staff can't take damaged goods, as there is often someone who ruins it by taking advantage of it.

In this school lunch scenario I would expect appropriate action would be to say staff are not allowed any. If there are any lunches left over after the kids have had theirs, then it should be given to a third party charity (e.g. a food bank) to dish out. And obviously if a kid wants to contact their parents, there are very few scenarios where this should be denied (I can't think of any).