I agree with Sandisw in regards to the QSDP. We did get this for free with a PIN, and we were never hungry. However, our party consisted of 8, 16 and 17 year olds who would probably eat more than your younger children. The kids meals are small though, so most kids will have no problem finishing it. Also, the kids meals do get boring for a child who enjoys variety. You would have to take a look at the menus online before leaving to find places to get variety. I thought it was on these boards, but I'm not positive, where someone posted the kids menu for all the CS's. I printed it and brought it with me as a guide. That way my son could get a variety.
I think it is wrong to substitute an adult meal for a child's, even if Disney does not distinguish between the two. Abuse of this will only increase prices in the long run, and for most younger kids it would be way too much food. If Disney is worried about this though, I'm sure that they could find a fix to it in their system. That is just my opinion though. We had plenty on our plate (especially at food court in POR) where we could give some to my 8 year old if he wanted to have something different. The same with desserts, I sometimes got what he wanted for my dessert and shared it just so he could have something besides the prepackaged chocolate chip cookie. However, with snack credits he was quite happy just being able to use those as he liked.
If you get a CS breakfast, it does not come with dessert, but instead you are allowed to pick 2 beverages. If you are at your WDW resort you will have your refillable mug making it 3 beverages really. For example, I would get a tea in my mug, then a bottle of OJ for breakfast and a Vitamin Water to bring to the park, or any choice in the refrigerator except for alcoholic beverages. Kids and DH liked the Monster Energy drinks with a retail value there of $3.99 I believe. The kids will get 2 drinks with their meal also, but they have smaller bottles of juice, water, plain or chocolate milk and can't think of what else there might have been. We did grab cinnamon rolls at Main St. Bakery (snack credit) and warmed them in the resort microwave for breakfast-yummy!
I know this is long, but we just came back Monday and all is still fresh in my mind. We did use all but one meal. I did use 2 meals just before leaving and got 2 sandwiches at our resort to eat at the airport. I ended up giving the bottled drinks to the bus driver due to forgetting that I couldn't bring them past security. He was happy though! We had so many snack credits left, so the day before we got fudge, pecan and cashew clusters, things on the idea of large Pixie Stix, and other packaged candy for the plane and home. It is nice having a those snacks back home. If you are worried about them melting, just pack them in your carry on luggage or any bag, and have luggage services hold them until you leave. That way no melting!
My final thoughts on the kids meals: Not enough variety, not so good chocolate chip cookie the only sweet dessert choice is poor, and no variety but grapes, french fries, and carrot sticks I believe for sides. I think at least some of the CS's could offer smaller versions of adult meals for little ones. However, you can find chicken drumsticks and sweet and sour chicken if you search the menus. As for the QSDP I found it to be worth it. Even though we brought home snacks that we wouldn't have, we would have spent more oop on just what we ate there. I am guessing on this just by looking at the price on the register at the time of purchase. I ate way too much dessert that I probably wouldn't have if oop, but it was nice not worrying about it.