I do believe that if a child asserts his or her will, a good parent must meet the challenge and make sure their will submits to Mom's or Dad's. However, call me chicken, but I have learned by hard experience not to create these situations because enough of them occur naturally. Therefore, my husband and I have chosen not to make food a battleground. Though we have had a lot of "showdowns", especially with a very strong-willed child who will remain nameless (you can narrow it down to one of three!), we have yet to fight a battle over food.
I also believe that children should be taught not to waste food. I've told my children about the "starving children who would love to have that food" just like you have. However, I have a different idea about waste, also from hard experience.
So there you have my disclaimer, now I'll tell you the "why" of it:
I am not a scientist or a doctor, but it makes good sense to me that if a child is fed good, nutritious food that they will eat what they need and stop when they are full. I also think that the amount they need varies greatly from day to day. However, there are a lot of obese children in the world. From my very unscientific observations, it seems that those children (barring medical causes, of course) aren't fed healthy foods and/or they are required to "clean their plate" at every meal. Studies have shown that unhealthy foods create cravings for more and children overeat that way. (Studies from my kitchen show that if you give a child a piece of candy, they will be asking for more in approximately 6.4 minutes.) If a child is conditioned that he must finish everything on his plate, he will eat it all whether he is full or not, therefore overeating that way. Food is "wasted" if it must be thrown in the trash can, but it is also "wasted" if a person eats more than they need for nutrition (then it turns to fat and all that other wonderful stuff--again speaking from hard experience).
So, what's a parent to do? I will tell you how it works at our house, and I would love to hear your comments on how it works in yours. I'm always looking for new ideas!
We try to eat fairly balanced meals (feel free to grade my menu on the sidebar--I know I'm not at an A plus yet!) and at regular intervals. For the most part, we let the child choose how much they think they can eat of each food. If they have food left over because they are full, we show them how to take less the next time because they can always get more and they don't want to waste it. Now, I usually don't have much to throw away (can't imagine what's going to happen when they become teenagers!). If it's a food they don't like, they have to try it but they don't have to eat more than a bite or two. Usually, they learn to like it eventually since we didn't make a big deal out of it, with a few exceptions (aren't there a few foods you don't like?). When we are not at Grandma's house :-), we don't allow pop (soda for some of you) or excessive sweets. When we have a huge stash of candy (like Easter candy....grrr), I keep it in a basket well out of reach and they have to ask for it. I try not to give them more than one or two treats a day. That way, they are usually hungry at meals. If they eat very little, I save their plate in the refrigerator and if they come asking for food, I give them the plate they didn't finish. That has happened about 2 or 3 times in the 7 years I've been a parent. That's about it...it's not rocket science.
The other day when someone took another helping of food with the comment, "I really shouldn't eat this, but..." (can't remember who, it was probably me