We love AKV and Kidani village, we have stayed their 3 times. As for Halloween activities, we have always done Mickey's Not So Scary Halloween Party at Magic Kingdom, but since you are arriving on the 31st, I believe that is the last night they do it, and it is most likely sold out.
The resort should have a list of activities (as mentioned above). The staff are great at AKV, I am sure they will have plenty of things for the kids to do. I do remember that in the evening they do a little show with the kids with african instruments and they just parade around the lobby. They also have the staff talk about the history of Africa, or speak about the area they are from in a room just off the main lobby in Kidani.
Enjoy, it is a great resort.