H.K.
How about since you have to invite all the kids in the class (both genders) you change it to a "knights and princess" party?
The kids could dress up as a knights or a princess (the boys would love playing wth foam swords) and you could host it at a park and set up medieval type games (think renaissance fair) or "boy vs. girl" games and serve lunch under a medieval tent. Or do crafts at the party... have the boys make swords and shields and the girls those princess cone hats with scarves coming out the top, or fancy crowns...
On the other hand I know I always like having a birthday or two in October to attend. Since these are usually costume parties my children get far more use out of their costumes than they would otherwise, so I think that is a fine option as well.
Have fun!