I have an 8 year old daughter who has never been sick for more than a day. She has never been to the doctor for any illness. I owe this to a nutritional diet, exercise, and education! Ever since she could eat solid food, I always made sure she had a wide range of nutritioanlly sound foods to try. Whole grains, colorful fresh veggies and fruits, 100% juices, lean unproccessed meats, and organics when you can get them! It isn't always easy shopping healthy- I am by no means rich! I work at a fastfood chain, and have for 10 years, and yet my family is always fit and healthy.
For snacks try things like wholegrain crackers and carrotsticks, or fresh fruits like strawberries or melon. Yogurt is a great staple! Make sure to look at how much sugar it has, though. Brown rice is very nutritious, cheap, and tasty. Combine it with chicken breast and sweet red bellpeppers, onion, and spinach and season it to your liking! Avoid salty, sugary snacks and meals...use herbs and lightly salt your cooking. Beans of all kinds are high in iron, protein, and fiber. Tofu can be made to taste like pretty much whatever you cook it with, has complete proteins, and low in fats. Younger children need more fat, remember, for healthy brain developement. Let your kids drink plenty of water instead of lots of juice or pop or milk. To get them to eat dark, leafy greens just put them on a sandwich with some turkey and cheese.
If they eat a high-fiber, filling breakfast, they won't need to snack so much. Oatmeal- easy, tasty, filling. Eggs and wholegrain toast and a glass of milk. No cereal! Cereal makes you hungry an hour after you eat it! They really only need 2 or 3 snacks a day- between breakfast and lunch, lunch and dinner, and maybe a small one after dinner but not less than 2 hours before bedtime. Breakfast should be the staple meal, with lunch following, and then a light dinner. Easy snacks are fresh veggie sticks, fruit, yogurt, string cheese, ovaltine, chips and salsa, veggiechips, and etc. My daughter LOVES cheese and fruit! Most kids do. Fresh veggies with a healthy dip are a favorite, and healthier than cooked veggies anyway.
I hope this was helpful!