I realize that's a simplistic answer, but it's true. Last year, we were 2 adults and 2 kids (ages 3 & 9). At TS meals, we always used 4 credits (2A/2C), because we decided it would be too complicated to try to save credits and then have to figure out where to use them. Besides, we only did 1 TS meal per day, and that was more than enough, food-wise and time-wise.
CS credits were trickier, because we never ordered 4 meals at once, especially at our resort food court. The kids usually shared a meal, and sometimes still had food left over. Sometimes I just ate the kids' and dh's leftovers, plus whatever leftovers we had in the fridge from the day(s) before. We didn't always agree on where we wanted to eat, so sometimes dh would order a meal and I'd just have some of his sides and dessert. If anyone was still hungry, we'd use a snack credit.
But we're weird eaters (dh is semi-atkins, I'm vegetarian), so this worked for us. Here's an example: dinner at Pecos Bill's was 2 burgers and fries, 2 drinks, and 2 desserts. The kids split one burger and drink. Dh ate the other burger, while I ate the bun (after a trip to the condiment bar, it was like a veggie sandwich) and some of each of their fries. The kids each got one of the desserts, which neither of them finished (but I did). Later, I got a spicy cheese pretzel with a snack credit. So we ended up with dinner for 4 for 2 CS credits + 1 snack credit. Scenarios like this are fairly typical for most people on the
DDP.
And snack credits were the hardest of all to use up. After all the food from the TS and CS meals, we were hardly ever hungry for snacks. When did get a snack, we almost never ordered 4 at once, or a lot ended up in the garbage.
In your case, since you still have one child who's free, it will probably be easier for you to use up credits, because the little one can just eat off the older one's plate (and your plate, and your dh's). But don't be surprised if you end up like many of us--in line at your food court on the last day with an armload of mickey rice krispie bars to take home!