To Kids, A Donald (Or Whatever other Character with a different suit) with a different suit, is not the same to the Donald they just met 30 Minutes ago, they view each Meet and Greet as a new Character.
Get an Autograph Book, I Can't remember where they sell them, but They Make tiny autograph Books for a decent price.
Don't Ride Haunted Mansion or Stitches Great Escape, If they Kid says they can Handle Haunted Mansion, then sure, not too scary. Don't do Stitches Great Escape, However it's pretty scary from a child's stand point, and it generally stinks.
And last, Fastpasses, Fastpasses FASTPASSES! I can't stress this enough, some rides have long wait lines, and if it's a ride your kid wants to ride, but it has a crazy long wait line, Get some fastpasses, every year when we go, we get them, and they are lifesavers.