Hi Andrea!
Thank you for sending in this question to the Moms Panel. The only Character Dining Experience in Disney's Hollywood Studios is
Playhouse Disney's Play 'n Dine at Hollywood and Vine. They offer a breakfast and lunch buffet. Characters are subject to change at any time, but the last time I was there for breakfast (fall of 2009), the characters were JoJo and Goliath from JoJo's Circus and June and Leo from the Little Einsteins. If your children are familiar with those characters then I think that would be fine, but if your children are like my boys, then the 6, 8, and 9 year old may have outgrown those particular characters.
In my opinion, a better alternative for breakfast near Disney's Hollywood Studios would be the Character Breakfast at the
Cape May Cafe in the Beach Club Resort. You can get to the Beach Club via a boat from the Studios. However, take would take a lot of time out of touring the Studios, so I wouldn't recommend it unless you had your heart set on a Character Dining experience near the Studios.
There are three great Character Dining Experiences near the Magic Kingdom, so that may be a better choice for your family: Chef Mickey's in the Contemporary Resort, 'Ohana Best Friends Character Breakfast in the Polynesian Resort, and the Crystal Palace in the Magic Kingdom. Since you can reach the Contemporary and the Polynesian via the monorail from the Magic Kingdom, it would be easier (faster) to visit those two hotels than the Beach Club from the Studios.
Have a magical vacation!