Melanie, at dietriffic, recently offered some tips on making a weight-loss diet work. I know that keeping track of portion sizes really makes things easier. I actually bring measuring cups to the table. These stainless steel cups belong to our "for the table" set. They make it easier to serve everyone the right amount. One cup of rice, one half cup each of two vegetables, a 3-oz serving of meat, and one cup of salad on the side. That's two grains, 2 ½ cups of vegetables, and our evening protein portion. A handy chart on the 'fridge (see below) reminds us what we should be aiming for in a day. Using standard portion sizes makes it all "deal a meal" easy.
source: MyPyramid intake patterns, MyPyramid customized dietary guide, DASH diet guidelines
I know that my 8 year old has had 1 serving of grain at breakfast, two slices of bread at lunch, a granola bar for afternoon snack, and only needs 1/2 cup of rice at dinner. The four-year-old only had one slice of bread at lunch, and so might want a whole cup of rice at dinner (but will probably get full, so I'll start with half a cup). They both get 3 half-cup servings of vegetables at dinner, which is good since the 8-year-old had 10 mini carrots at lunch. The three (or fewer) ounces of meat they will eat with their dinner goes with the bologna or peanut butter they have already eaten today to give them the protein they need.