The farmers around me (lots and lots of them, live in a rual area) do wear a lot of overalls (especially the older ones), flannel, steel toed boots (usually really rough-looking leather boots), jeans (wrangler seems to be popular, lol), t-shirts, and they all wear hats of some sort. The woman will frequently wear straw hats because they don't want the sun to burn their face, ears, and neck while leaving their foreheads a dozen shades lighter, lol, the guys don't seem to care although my dh has been known to put a bandana on his head and then put his cap on over it, depending on what he's doing.
But I would dress my dd in jeans, white shirt, and bandana belt because it's cuter and it fits in with the farmer look.