Surely the idea of lunch is to keep the child full and energy boosted until home-time?
In which case, a lunch high in sugar and processed food is not going to do the job. Our school have what I would call a balanced approach to the school lunches - a large mix of different foods and they don't add salt, and handmake their pizza.
I don't understanad the policy of labelling food as "bad" anyway whether at home or school.
Squash is not necessary unless your child has sensory issues or other issues raised by having SEN but these would have already been raised with the school surely? I cannot imagine why you wouldn't?
my child would choose squash over water but as he is thirsty, he drinks water!