So you'll have 3 "adults" (the 13 year old is an adult for Disney purposes), 3 "children" (3-9) and one under 3 who is free? Oh my yes, you will have enough food.
TS meals will give you an insanely ridiculous amount of food. Seriously. At buffets and family-style meals, your under 3 would eat as much as she wants for free anyway. At regular TS meals, you'll have 3 kids' appetizers, 3 adult appetizers, 3 kids' entrees, 3 adult entrees, 3 kids' desserts, 3 adult desserts and 6 beverages, of which many restaurants will let you order "specialty" drinks such as smoothies, milkshakes, virgin pina coladas, etc. Your little one doesn't stand a chance of going hungry at any of your TS meals. I'd even recommend splitting meals because you'll have so much food, but then you'd have credits leftover and frankly, I can't imagine wanting to have more than one TS meal per day.
CS meals will give you plenty of food. At lunch you'll get the 3 kids' meals, the 3 adult meals, 6 beverages and at least 3 real desserts (maybe 6, if the kids' meals don't include a "dessert," such as jello). You'll probably find you don't want to use all 6 CS meals at once, which will give you extra credits for breakfast (which includes juice as your beverage but no dessert). Add in the 6 snacks a day your family will get, and unless your kids are bottomless pits of hunger (maybe the 13 year old . . . ), you will have plenty.
There were 4 of us (2A and 2C), and we ate like kings (or was it pigs?). My dh used a CS credit for breakfast almost every morning (kids and I hit the parks early, breakfast bars in hand--though we could have used 1 snack credit at our resort gift shops for a box of 12 donuts instead), then we shared 2 of the remainder (occasionally 3) for lunch. We usually got one dessert and one fruit, giving us something healthier to snack on between meals. We also had lots of drinks leftover, since we got big bottles of juice and chocolate milk with our meals, and would usually split one and put the other in the fridge for later.
We were rarely hungry for snacks, but did try to use those credits whenever we could. Dole whips, pretzels, ice cream, popcorn, main street bakery, etc.
At the end of the (10 day) trip, we left several beverages in the fridge, and still had a couple of CS and 10 snack credits left. But it was an amazingly relaxing trip, knowing that all the food was already paid for and everyone could order anything they wanted. Good luck, and have fun!
