Why not get them involved in packing their own lunches - give them a set of healthy options and let them choose which ones they like the best. Perhaps there are just some things they don't like or have a taste for yet. I remember one time I spent the night at a friends house, and his mom made my lunch for me that morning - my folks must have told her that I pretty much eat peanut butter and jelly every day for lunch - but she instead made me some orange jam, no salt no sugar natural peanut butter, on some sort of rye bread. These days I would eat something like that, but as a kid I was like "what the hell?" and miserable with it at lunch. I think I ended up hitting the vending machines that day instead with what little change I had.
The school lunches when I was in school in the 80's were basically just TV dinners in foil containers that they would bake in large quantities and serve with a small carton of milk. Most of the time they were pretty gross but once in a while they looked good. We also had a bit of a treat though on Fridays since my grade school (it was Catholic) would sell home made pizza's on those days, along with "pizza fritta's" or fried dough tossed in sugar. So instead, for lunch we would each get a half of a 12 inch pizza. Or you could just buy two slices for yourself, but most of us went with the half pizza, lol.