I have 2 DDs who were almost 5 and 6.5 when they went to the Tea last time. They loved it. Now they will be 6 and 1 month from being 8 when we go to WDW in March. When they found out we were going to WDW, the first thing they asked about was the Tea. I don't think there were a lot of 8 and 9 yro, but there were definitely a few, and like I said, my older one can't wait to go again. There were only a few boys, but they had fun. When my kids were there, they decorated their own cupcakes, ate them and pb sandwiches and drank "tea". They also played games (my kids can't remember what the games were, except that they were up and about playing them.) Then they also made a paper flower bouquet for their moms. I think your kids will love it.
By the way, I am not sending my 3 yro DS (he just turned 3 a week ago). He does not separate well from me in strange places yet. Give him another 6 months and he will be going too.