With kids as young as yours, Kim, you might want to limit your more formal character experiences to about two or three. And by "formal" I mean, paid (meals, for example). In spite of the fact that your little ones are head over heels for Disney characters, you might find that they're a tad more timid when aforementioned characters are larger than life right in front of them. Many children, especially babies, are actually quite frightened of the characters and I certainly don't blame them; Mickey is easy to love when he's two inches tall on the TV screen, but it's a whole different story when he's grown-up size in the parks! By limiting the experiences you're paying good money for, you'll give your children the opportunity to meet and greet if they want without really spending a fortune on something they may or may not enjoy. If you find that your kiddos are taking well to the characters, you can certainly make plans to see them in the parks; there are plenty of opportunities to do so!
Plan on each character meal lasting at least an hour. I've been to a couple that lasted closer to two. My personal favorites as far as character meals, are
Garden Grill and the
Supercalifragilistic breakfast at 1900 Park Fare. In my experience, we've found those two options to be a bit more low-key and less overwhelming than, say, Chef Mickey's. One last tip for you: often times, "face characters," like Alice in Wonderland or any of the princesses, are better received by little ones who don't fare as well with the costumed characters. Good luck!