Here are more core strengthening exercises which focus on the obliques that you, as a youth baseball coach, can use with your players.
To work the obliques, athletes should lie on the ground and tilt their knees to one side, so that their torso faces the sky but their knees face the side. Athletes should then to do regular crunches. Instead of working the top of the muscles, like normal crunches, this works the oblique muscles. It is especially hard to keep the head and arms from curving inward on this exercise because it is much more difficult than traditional crunches, so coaches need to watch for athletes whose bodies droop down. This shortens the oblique muscle and gives it less of a chance to lengthen and contract.
The last abdominal exercise is called the bridge crunch. Athletes should begin with their legs in the normal crunch position. They should push up, so that their shoulders are on the ground but their hips and knees are in the air. From this position, athletes should attempt to lift their shoulders like a normal crunch. This is very hard to do, because the weight is down near the shoulders, so athletes should not be expected to do more than 1 set of 15.
These moves can be changed and modified as necessary or as desired to change the amount of work the muscles do. As a baseball coach, you can put together different programs.