Generally, no we don't find the portions large enough to share. I also find I tend to eat more at Disney than in my usual day to day life. Probably because I'm burning so many calories with all the extra walking. The only time I feel stuffed are after certain buffets.
ETA: As for kids meals, my boys easily have always finished the kids meals at QS locations, but not always at TS meals. Still wouldn't be quite enough for them to share though. My younger ones are big eaters, my oldest is not.