My parents used to make my sisters and me clean our plates. It was miserable - meal time was a battle, instead of nice family time. Then when I was about 10, we were at the dr's for a check up, and my mom pretty much ratted me out, saying "melanie won't eat the vegetables i serve, fish, etc" (i WAS a picky eater).. and the dr. gave great advice: "your daughter is a healthy, happy girl, at a healthy weight, growing at the right rate, etc - she is clearly eating what she's craving, and it is working.. by forcing her to eat things, you are over-riding her body's inner-workings and may be teaching her to overeat"..etc..
I have kept to that throughout my life - at 33 years old, I've never had a weight problem - I go through periods of craving carbs, proteins, and yes- even veggies - I follow what my body tells me, and it works..
Now I have a 2 and a half year old daughter-- at mealtime, i use those dishes with 5 seperate sections- and she has a choice- 2 servings of some kind of fruit and or veggie, some kind of carb (pasta, potatao, bread, etc), a protein (she refuses to eat meat, so i offer eggs, cheese, yogurt, beans,), and the last - and largest section is what the rest of the family is eating - "the grownup food".. I can clearly see what she needs on any given day b/c one day she'll inhale the banana and say, corn - and avoid the carbs and protein altogether.. Other days, she's all over the proteins..
Let their bodies be their guides-- of course -- all bets are off when you introduce ice cream and candy - their bodies will ALWAYS tell them they need that!!! lol