Line up your players to your left and have the first child run on a diagonal in front of you and you toss them a fly ball just like a quarterback throwing a pass to a receiver. Use tennis balls if your players are young/inexperienced. Stress they run on the balls of their feet, keep their eyes on the ball and they use two hands to catch the fly. You can have them catch many more fly balls this way than hitting the balls off the bat.After going through on the left side, have them switch to your right side.