If the school took away anything you packed your kid for lunch, then they vastly overstepped their authority, at least in the U.S. I'm surprised Canada would allow school officials to have that much authority over their student's lunches as to allow them to confiscate food or drink they deem unsuitable. It's certainly not the case in the U.S.

HNSB, I presume you've met school-age kids before. They lie whenever they think they can get away with it, and often even when they can't, and take every advantage they can find. I know several kids who are in grade school to middle-school, and a couple who are about to begin pre-school, and I remember from my own time at school that kids who regularly brought lunch from home would throw that lunch away or hide it and claim they hadn't brought any when it was pizza day or chicken nugget day for school lunch. Complaints about the packed lunches and trading between students for the stuff they brought or the stuff that was on the menu was and is also common. Put yourself in the shoes of a 4 or 5 year old, who's mom packed you a plain old turkey sandwich for lunch, when you learn that chicken nuggets are on the menu for the school lunch. Every 4 or 5 year old I know would do anything they could to get those chicken nuggets instead of having to eat that sandwich, including lying, whining and generally making a big pain of themselves if that's what it takes. Now, imagine how mad your mom would be when she learns you didn't eat the sandwich she made for you, and instead ate a couple of chicken nuggets off the school lunch which she now has to pay for. Would you tell her that you made an ass out of yourself until they gave you the chicken nuggets you wanted, or would you tell her the school lunch lady made you eat them instead?

Which is the more likely explanation here? That a pre-school age kid really wanted to eat her turkey sandwich and banana, but the school nutritionist made her eat chicken nuggets instead, or that a pre-school age kid who has a turkey sandwich from home sees chicken nuggets on the menu and makes enough of a fuss that the nutritionist just gives her a school lunch and sends the kid home with a bill for $1.25 and a form letter about school lunch supplements, and when the mom gets mad the kid blames the school nutritionist?