This is one of many kids baseball drills to teach proper hitting techniques in different situations. Knowing how to hit each of these balls is going to give the younger players an idea of why they are supposed to swing the bat the way they are instructed.
What you need (set up): You need a tee with a ball, batter (with helmet), and you can have a few fielders to shag balls.
How this drill works: You can demonstrate to the younger players what happens when you hit certain areas of the ball. Also you can show the players what happens when you swing a certain way (up, down, level).
Give each player the opportunity to hit off the tee and see what happens when they hit certain parts of the ball. Further, allow them to experiment with different types of swings.
Results: Once the younger baseball players understand what happens when they strike the ball in certain areas, it will be easier to impart on them that you want them to strike the ball in a downward fashion in order to create more grounders.
Many of them will want to swing for the fences, because home runs are the cool thing to do, but ensure them that once they can make contact on the ball wherever they want, then hitting for the fences is just around the corner.