One of the things that our 12 year old kids really like to do are “play” with non-softball equipment. During our indoor sessions, we take practice “swings” with a medicine ball for our indoor softball batting drills.
The batter holds the ball with two hands and makes a good swing throwing the medicine ball to his partner. The kids added a penalty for dropping the heavy ball or for a bad toss, ten push-ups. The key is to make sure they are swinging their arms and ball in a good swing plane and using their hips and legs to put the extra push into the swing.
The kids really enjoy it. Another variation is to see how far they can throw the medicine ball. Again, the focus is on the power from the legs. All of these abilities will improve their softball skills.