My son did this last Sept. He was 3 year old, which was allowed at the time. (They have since changed it to four to bring it in line with the other children's events.) He LOVED it! It was the highlight of his trip. He still talks about his tea party with Allice and the Mad Hatter. If you click the photo link in my sig and look at our pictures from Sept. 2006, there are several in there from the event. They let you go in, get your child settled, snap a few pictures, and then they toss you out. I spent the time exploring the shops and grounds at the GF. My son had no issues with me leaving him, which I knew he wouldn't when I booked it. He LOVES other kids and the idea of having a special kids only party made his day! I think there were two or three other boys there that day, but that wouldn't matter to him anyway. He wouldn't have minded being the only one.
Just a few weeks ago, we went to Disney again and he did the pirate cruise this time, because he is 4 now. He thought that was the most amazing thing that had ever happened to him - but he still talks very fondly about the tea party.