One thing I'd say is that you don't want to book too many character meals. They are fun, but not quiet and relaxing. I've said this before. One or maybe two per trip is good, but the rest of time our family prefers quieter meals. Chef Mickey's and 1900 Park Fare were especially LOUD - the entire meal. CP can get fairly loud too.
You keep getting up to get food at the buffets, trying to watch out for characters, scrambling to take pics and get autographs signed when the characters come by. Trust me, they don't stay at your table very long. If you should forget an autograph, too bad. They won't let you go to the characters when they are no longer at your table. So they are quite chaotic. One more thing, although you do get a fair number of pics, they all have plates of half eaten food in the foreground. The character greeting spots elsewhere in the parks are more picturesque.
As others have said, it depends how the little ones react to the characters s to whic are going to be best. Princess is a good choice especially for little girls. Chef Mickey's is a good choice for characters as Mickey is likely to be one of the child's favorite characters.