When we went to Disney last Christmas we had the dinning plan for my son who was 4 at the time but not my daugher who was 2. Honestly, most of the time she ate off our plate. You get a TON of food with the regular dinning plan and there was plenty for her to eat, but she's not a picky eater at all. The quick meals are the easiest because you get an appetizer (fruit, yogurt, things like that), your main dish (pizza, sandwich, depends on where you are at) and a dessert. It was really easy for her to eat, especially since she was 2 and didn't eat that much.
When she did need her own plan then we just purchased one for her, but it was on the rare occasion that we did that. If you have 2 little ones then you can probably do 1 dinning plan for them and have them split it. You CAN get them a plan, it just might be a little wasteful for them to have the quick meal, the full meal and then the snacks. We had so many snacks left over from ours that we stocked up for the car ride home.
For any sit down meals you want to eat reserve them as far in advance as you can, I want to say that it's 6 months in advance you can do that because the best placeses WILL fill up. We called the day we could reserve and places that we wanted were booked. Also, make sure to pay attention to the places that cost 2 sit down meals - like Cinderella's Castle. You can use the plan, it just takes up 2 of your meals. There are a lot of buffets as well and they never charged us for the children on those.