My dck's are extremely small eaters compared to some of yours lol. They never complain about being hungry in between lunch and snacks and they are all of average weight except one who is not huge but is bigger than the other kids. They can only eat as much as you serve so I would suggest cutting back on that. I even have kids who give me their plate when they're done and there is still food left on it. I have only had one child who didn't have that "I'm full" trigger and he was the biggest child I had.

I would guess that mine eat about 1/2 to 1 cup of food for snacks(as an example, half a banana and 3-4 crackers or a piece of toast with 3-4 strawberries) and about 1.5 cups-2 cups of food for lunch (today was homemade mac and cheese with broccoli, carrots and cauliflower mixed in, fruit salad and a yogurt cup)

I can't even eat 2 bananas so to me that is excessive for a child. I will dish out lunch and if there is extra's and not enough for another meal than I hand it out but usually once it's gone it's gone. I am overweight so I think I am more conscious as to how much I give the kids because I don't want them to be overweight.