At least a little of each food must go on their plates. They can eat or not eat, but they can't whine about it. I try really hard not to urge the picky one to eat more, but sometimes I forget. We have dessert, or not, regardless of what they eat, although usually it's just fruit.

I have a very picky 6-year old. I don't have any 'rules' per se, other than saying Grace before eating. I have no requirements about my son trying everything or eating so many bites. If he eats, great, if not, his choice. I will refuse to provide seconds on his favorites if everything else has gone untouched. Sometimes he'll decide to try something else, sometimes not.
Also, my son always gets a snack before bed, but it might just be cereal if supper wasn't eaten, rather than a treat like a popsicle.
I grew up with the dinner time battles similar to the pp description of her battles with squash. I will not be repeating that history with my son.

1. You are in charge of your own tummy.
2. If you get down, you're done.

I'm an Ellyn Satter follower (with some modifications -- no bread or dessert on the table). I put out the food on their plates, and they eat whatever of it they want. No food until the next meal/snack time.

My exact rules are as follows:
1. Wear clothes (top and bottom) to the table.
2. No crying at the table. If a meal makes you cry, go do it in another room.
3. Ask to be excused and clear your place when you are done.

I find that when I get after anyone about eating anything, they exert whatever control they have to keep my attention. That usually means not eating whatever it is. Therefore, each person is responsible for his or her own food.

We do have several options going at a time because I am a vegetarian and the rest of the family eats meat; so far, no one has gone with my meal plan to date, but our oldest is only 6!

I'm the 10:49 post-er.

Want to say something about kids refusing to eat certain things.

My memory of my childhood is that I ate almost everything. Very, very few things were on my "yuck" list (pickled beets and brussels sprouts were two of them).

So when my preschooler became a picky eater, I was confounded. "Really, you only like ONE kind of mac-n-cheese?" "Wait, you hate ALL vegetables?" "Seriously, you had to barf when you smelled the asparagus?" Heh.

But we found a few healthy things that she does like (whole wheat versions of starches, black beans, cucumbers, banana-and-buttsquash "pudding"), and to tbe best of our ability, we limit access to outright junk food.

Our preschooler truly refuses to put things she doesn't like in her mouth, and she really will choose to go hungry rather than eat a "yuck." Absent force-feeding her (how obnoxious is that?), we had to work around her aversions. So we do, to some extent, "cater" to her palate, meaning we try to have at least one child-friendly calorie-dense healthy option at the table that we're almost certain she'll eat.

But (healthy) dessert is only an option if she eats a mommy-and-daddy validated healthy, well rounded meal.

Thedinnertime stress is much better, now.