Scavenger Hunt
For smaller groups of children, hold a scavenger hunt. This works especially well for a party that's held at home in the backyard, at a park or at any location where preteens can have some freedom to walk around. Adding the element of photography significantly opens up the potential for item lists. In a photography scavenger hunt, participants find the items and photograph them instead of bringing the items back with them. Middle school students should have a blast getting to pose with the various items.
Beach Ball Questions
Play a game that gets the pre-teens interacting with one another while learning interesting facts about people. You'll need to prepare a beach ball beforehand. Inflate the ball and use a permanent marker to fill the ball with questions the participants should feel comfortable answering in front of a group. Things like favorite foods, songs and school subjects along with hypothetical things like "What would you do if you could read people's minds?" all make good potential questions. One person starts and throws the ball to someone. The person must answer the question closest to her right thumb and pass the ball along to someone else.
Active Game Party
Young adults in junior high school usually have tons of energy to burn off. Make the entire party one that focuses on a game. Pick a sport or event the child enjoys and find a party location that offers instruction or organized birthday parties. Bowling allies and arcades are traditional choices with a game focus, but you could find something like a hockey rink or basketball teaching center where the kids could get pointers in the game and play an organized match at the end.
Drama Bag Game
For a birthday party with outgoing, creative junior high students, play the drama bag game. Divide everyone into teams of three to four people and give each one a shopping bag that contains five items. Item ideas may be a toothbrush, purse, pair of shoes or article of clothing. Give the teams 15 minutes to create a skit, song or commercial that uses all the items from the bag. After the time is up, each team gets to perform for everyone.