My favorite lunches as a kid were after my parents had a party- I'd have leftover spinach dip with crackers and crudites! Yum! Ooh! Another favorite was when mom would take a green apple, halve and core it and fill it with peanut butter and close it back up again. I still eat those! She also used to do sandwiches w/ one slice of white, one whole wheat, cut out a heart or a star in the middle and flip it over so that one side would be brown w a white heart and the other would be white with a brown heart. I loved that!
I also liked soup, chili, leftover stew or pasta or stir fry etc. in a thermos.
Cold grilled steak or chicken with steak sauce or bbq sauce to dip.
Yogurt with granola and fruit chunks on a drinking straw "kabob" (that won't poke someone) to dip in it would be good.
Peanut butter on a rice cake with banana slices is great.
This is a snack for me sometimes: Take a breadstick or pretzel rod, wrap with turkey or ham, cheese if you like, then a leaf of lettuce. You could add mustard or mayo, but I eat just the ham and lettuce on an onion-poppyseed breadstick. It's so good! A few might make a nice lunch.
You could pretty much pack anything your children like, from pizza to quiche to shrimp cocktail! - some might just take some finagling. Use thermoses, cold packs, etc.
I would also buy some plastic silverware or get a cheap set for kids. Kids lose things and good silver can be hard to replace.
Almost forgot this:
If you find that foods in a thermos cool down too much, simply fill the thermos with boiling water and let sit for 5 minutes or so, then dump out the water and fill with your soup, chili, whatever. It will stay hotter. This isn't a good tip for younger kids who need the "warm not hot" foods.