You could get a well insulated thermos for each kid and pack things like soup, macaroni and cheese, casseroles, rice dishes, spaghetti, or scrambled eggs in them. You can freeze a juice box or cup of yogurt/pudding and put it in an insulated lunchbox to keep perishables cold (like lunchmeat or string cheese).
Personally I'm a big fan of the laptop lunchbox (
www.laptoplunches.com), but if a kid cannot refrigerate or heat things up, it may not be an everyday option.
My kid's just shy of three, but the plan (and we'll see how well this works out...) is to let him pick out one lunch a week to eat at school when the monthly menu comes out. The rest of the week would be packed lunches.
Parents Magazine and Cookie Magazine both have really good ideas for lunches, you may be able to find more ideas from either of them online or skimming the magazines for free at the library.