Some great advice from Rachel Goodchild

TRIUMPHING OVER FOOD BATTLES
1. Look ahead. No one wants an adult who only eats chicken nuggets. Children need at least seven attempts to a food before liking it (if they don't immediately) The first tip is to not give up offering healthy options. I found my girls won't eat salad as much when it's all put together, but if I place all the ingredients out on a platter, they'll eat far more. We also use the "I'm sorry, but the mango in the salad is only available with the rest of the salad, and you need to eat it if you want more mango" That's turned all three of my daughters into regular lettuce eaters :)
2. The nothing sandwich is a great resolver. If a child refuses to eat the meal you cooked the family, it's a nothing sandwich (plain bread). It won't kill them, and it's enough to stop being hungry, but not that nice that it's preferable over time. That's it. No extra food.
3. If they snack through the day and keep on raiding the cupboards and it's driving you spare, work out what snacks you want them to have through the day to snack on (so two pieces of fruit, one to two biscuits, and maybe a packaged treat such as a muesli bar, and perhaps a vegetable) and let them choose from the fruit boal, and fridge and cupboards what they are going to eat, and place it all in a lunch box. Then THAT IS THE ONLY PLACE they can eat from. Often they'll eat it all by nine the first day. STAND FIRM. They'll learn to pace themselves once they figure you are not going to budge!
4. Remember children are born with a drive to survive. They won't starve to death. You don't need to bend over backwards to make them eat. You may need to stop giving them so many options, and just telling them it's an apple and cheese sandwich or nothing. If a child says they are hungry and won't take an apple or banana... they probably aren't that hungry. - they are just munchy
5. Give them independence around food. Let them butter their own toast, or put their own cheese and tomato on thier crackers.