Okay! Your DD wants to meet the most characters? There are spots in each park where you can meet many characters at once!
At Magic Kingdom, if you get there before noonish, there are usually many characters right after you enter, between City Hall and Exposition Hall. You can't miss 'em! The characters are all over, so look around! Some are in the center circle, and some near the buildings.

If you don't see many, wait a few minutes and some more many come out.
As another said, also go to the ToonTown Hall of Fame. It looks like a gift shop between Mickey and Minnie's House, but it has much more! There are these roped-off lines to the right, and these lines lead to three rooms with characters. Usually there is one room of princesses (Cinderella and friends), one with Pooh and friends (usually Eeyore and Tigger), and I think some classic characters in the third room. Also check the front of the Castle - characters meet there often throughout the day. The Times Guide (with your park map) usually lists when they are there.
At Epcot, the most characters can be found on the "Characters on Holiday" bus. It's a big red bus that makes various stops in Epcot. There can be about 12 characters on it. The Times Guide lists where and when it stops.

It's last stop is usually around 4:00.
At Animal Kingdom, there are characters right when you enter, between the bag search and the turnstiles. They meet on and off throughout the day. Also Camp Minnie-Mickey has Mickey, Minnie, and Goofy and probably a few others during the day. As another said, if you head to Dinoland, there is a dock where Pooh and friends meet throughout the day.
At MGM, there are two good spots (if nothing has changed by now!). One is near the entrance, usually in the late morning/early afternoons. The characters meet there once every hour, for about 25 minutes. I can't remember if they meet at the top of the hour (like 12:00 or 1:00) or on the half-hour (12:30 or 1:30). They are done for the day around 2:00 or 3:00 (can't remember which). We seen up to 12 characters at once here! The other good spot is the Big Hat at MGM, where characters also make appearances once every hour, for 25 minutes or so. They also meet here in late mornings/early afternoons, and stop around 2:00 or 3:00. Sometimes they will have another meet in the late afternoon after the parade, but not always.
This was probably way too much information, but character hunting is so much fun! Hope you find enough characters to make DD happy!
