[Cavey]

Character meals are booked the same as other WDW restaurants. When you call WDW dining, you can cancel one reservation (ADR) for another.

Now, you didn't say which character meal you are interested in. If you have boys (or a mix), my personal favorite is Chef Mickey's in the Contemporary Resort a short monorail ride from the Magic Kingdom. Mickey, Minnie, Chip, Dale, & Pluto are always there. Goofy & Donald switch off between breakfast and dinner.

If you have girls who want princesses, I would recommend the Princess Breakfast at Epcot (in the Norway pavilion).

If Lilo & Stitch are your favorite characters, Ohana has them at breakfast (I have not done this meal, as I LOVE Ohana for dinner.).