This is where modern conservativism (i.e. the victim-mentality) meets the "personal responsibility" mentality (aka a more classic conservative mentality) and ****s the bed.
On one hand, a conservative would supposedly believe it is a parents duty to take personal responsibility over their child's nutrition. I do. My son could receive food at his day care, but instead I pack a lunch because I want him to eat what I want him to eat.
Here's the facts as I see them: If you decide you want the school to feed your kids, then you give up the right to complain about what they are fed.
If the school is providing the food, the food should adhere to reasonable health standards. If the parents are providing the food, it can be a tub of ice cream and piece of buttered cat **** for all I care.