Good advance drill is have the kids use the wall and use one hand on their stick, going to have to use your right hand if you are a right-handed player, your left hand if you are a left-handed player. Basically, what I want to do is just have one hand on my stick, I want to go through my normal throwing motion as if my left hand was on, but I am actually take it off the stick, and as I throw, I get it out of the way and then follow through with my one hand.
Good thing to have in the mind when they do this is if you are a baseball pitcher, and you are going to trying to get your hands extended away from your body and focus again on one point on the wall. So I am here catching and throwing with one hand. Notice my off hand again, softer stick but it's in the proper position as if it were going to be a part of the throw, I am just going to catch and throw. It's going to work on snapping the top hand, which they should do for every shot and every pass.