OK, what if a school decided that no children should believe in God?
That they would start expelling children whose parents raised them in any religion?
There would be people here applauding such a move - saying 'it's good for the children and it's the parents fault for being religious, which is stupid and backwards.'
So why wouldn't that be acceptable? If it's acceptable to take most other aspects of the child's upbringing away from the parents? For the school to enforce its will over the will of the parents?
What if they started saying 'your child has to stop doing rugby and take up tennis instead.'
Or 'your child has to attend after school class as he's falling behind - this is not optional.'
How much power do we want to relinquish to the authorities? All of it?
They're only saying that they can't have junk food IN SCHOOL. All your other examples are acceptable within the school day, surely?