Looking at the Food Guide, children 2-3 should have 4 servings of fruits and veg. per day. 4-8yos should have 5 servings. If I'm reading it right, they still consider 1 banana or 1 apple= 1 serving just like with adults. Its just that their examples consider that children won't necessarily eat a whole serving in a sitting.
My group these days aren't big fans of raw vegetables so we just have them cooked at lunch mostly. Fruit is reserved for snacks. Mostly apples, oranges and bananas because I know they will get eaten quickly before they spoil, that can make your costs go up too, having to throw out food. I have also found that it is better to give smaller portions at first and allow seconds for those who want it. Instead of giving lots to start with and then throwing a lot out if they don't eat it.