Quick Toss for Bat Speed
This is just like regular soft toss where a coach or another player is positioned across the plate (facing the batter). They toss a ball into the strike zone to the batter's contact point and the batter is hits into a net or can hit out into the field where defenders can field the ball. The location of the toss is very important in soft toss drills because it's part of the batter learning where proper contact point is.
However in this soft toss drill, you would gather up a bunch of balls (half a bucket usually works great) and toss them one right after another. The batter will have to swing hit the ball and quickly get their bat back into position to immediately swing again because the next ball is being tossed. Half a bucket is plenty to start off with at first as you will see that your players will probably be tired by the time you get to the last few balls.
You don't always have to use regular softballs, you can also use wiffles or tennis balls, etc.
With younger batters you may find that they throw all mechanics out the window in effort to hit every ball. Therefore, with younger batters especially, you must watch the how quickly you toss as well as how long you run the drill. Half a bucket may be too much. Again, you don't want the speed of the drill or the length of it to cause a serious break down in their swing mechanics.