I play high school ball and we use one hand, when you catch you can use two hands but its for safety, becuase if that players hand gets hit with a fast pitch you could get hurt. And this is coking from a catcher that got her teeth knocked out by a softball at age 13.
A good one that my coach used to do was this:
give then 3 balls to throw around between right center, and left field. And if they drop all three within 5 minutes they have to run a foul pole.
Does anyone in the central Florida area need help or want to practice? Im, a high school softball player and I can help if anyone has younger kids that need help! I catch and play outfield, and infield.