When I made my reservations for our trip last June, the CM did say that my dd1 would have to eat off of my plate and that we would be charged the kid's meal price if she had her own plate at buffets.
In reality, we had so many different plates going at our table (salads, main dishes, desserts, etc) that it was hard to tell which plates belong to which people. Also, my dd1 still flips her plates over...so taking messy mats are a good idea. These are just those sticky plastic placemats that you can put on the table for your dd1 to eat off of. No issue for Disney, no broken plates, and a clean eating surface.
Also, we have always ordered a drink for dd1 (usually milk) figuring we would just pay extra for it. We've never once been charged...so I guess drinks for kids under 3 really are free!