Keep the practices moving. Do station drills with the help of assistant coaches or parent volunteers. Encourage the help of other adults when coaching this age, since attention levels need consistent monitoring. Drills can include practicing ground balls, soft-toss hitting against a fence, fly ball catching, sliding drills, and live batting practice in a cage. Blow a whistle every 10 to 15 minutes for stage rotation.
Allow the kids to try different positions. Rotate taking grounders at all the infield positions with all the kids. Have all kids shag fly balls. However, limit pitching and catching to players you identify with the skills to handle those positions. Don't embarrass a young athlete with a weak arm by making him try and pitch if he's not ready.
Take care of the kids at this age. Limit how much they throw the baseball. Watch pitchers especially. At this age, their pitch count in a game should be limited to 60 to 75 pitches. Do not allow them to throw a curve ball until they are at least 13, and limit how much they throw this pitch. A curve ball can put strain on the elbow if thrown improperly, especially at a young age.
Encourage positive thinking. Teach the kids to visualize positive outcomes, like hitting the ball up the middle, catching the ground ball and throwing straight to first base. Challenge them to encourage each other when a good play is made. Consistently encourage the players yourself during practices and games. Middle school kids need plenty of positive reinforcement, and they look up to you as a coach. Make the most of the responsibility you have been given.
Create fun batting drills. Have them soft-toss dried butter beans to hit with the bat. After swinging at the small objects 20 or 30 times, show them how big a baseball now looks. Hit soccer balls off a batting tee to increase power in their swing.