In fairness, squinting my mind a little, I can understand those misconceptions. I certainly wouldn't have known what kind of climate cotton needs to grow, though if I was driving by slow enough to make any kind of guess at the crop, I like to think I could distinguish it from corn.
As for cows, well, if these kids are lifelong city dwellers who've only seen pictures in books, I guess you could make the wrong assumption about the animal's size. If you're not given a proper frame of reference, I imagine it could be hard to tell. Seeing cows on TV can't be all that common really, unless you've gone out of your way to watch a show about farming.
Not knowing where your meat comes from though - I'd say that's far less forgiveable. Basic human curiosity would prompt you to seek those answers at your earliest opportunity, wouldn't it?