In years past, there were more characters simply walking around the park (in my opinion) but it was neat this year because they had the good guys and the bad guys in two different areas which helped some to cut down on the congestion (which was AWFUL!!!) However, your children will have a great time!
Go past the little mermaid towards WWTBAM and that is where all the bad guys were hanging out. You can get pictures made with a variety of characters including Darth Vader this year! (DV is where Sor. App. Mickey usually is - and we went there first and got throuh the line in about 20 minutes - it was a really long line every time we passed by there after that). We saw sand troppers just walking around, the all white female bounty hunter type that I THINK was in the pod race shooting at the pods from the side of a mountain, the Emperor and his royal guard, Darth Vader, Zam WEssel, and Boba Fett. (there were probably more, but this is what we saw)
Over near Star Tours, you will see the stage the above poster showed in the picture. This is where they gather after the parade, they do the Jedi training (get there at the end of one show and your children will be right at the front and will probably get picked if they act excited for the next show) and each child gets to fight either Darth Maul or Darth Vader. They do some silly other shows there as well. In this area are the "good guys". We saw Anakin, Mace Windo, Kit fisto, Shak Ti (forgive my spellings), Chewie, Ewoks, Queen Amidala, and Jedi Mickey (he is in Dangerously Stupid studio - a little bit of a wait, but not bad).
There is a parade at 11:15 and a couple of the sessions of WWTBAM are set up to be STar Wars specific. You can get a schedule of events with the park maps when you walk in.
All the characters are either in lines where you wait your turn like normal character greetings for autographs and photos, or they are walking around and MOST of those will stop for pictures at a minimum.
Its a blast for the Star Wars fan. There is also a movie that shows how some of the wonderful ideas for III were created and developed (about 1/2 hour I believe - worth it for the SW fan as well).
Have fun!!!