My favorite drill is more of a test than a drill. I do this drill at the end of practice right before a game day. I do this to determine if my infield is ready for the game. My 8u team turned several double plays this season after I started using this drill. Teaching eight year old girls to make a fast throw to first after touching second is not an easy task. I think this drill made that possible.
You start off with your infield in position including the catcher. This drill can be done with the outfield in place also. You will need a bucket of balls and a Fungo. (I use a garden variety bat) Make sure you know exactly how many balls are in your bucket before you start the drill. Go quickly around the horn and always mix up where the play is and where the throw is going to keep them on their toes and keep them sharp.
You start out by telling your players where the play is going, i.e. Plays at one or first. Then hit a ground ball to any position on the field, i.e. the second base, the fielder fields the ball makes a throw to first. The first baseman relays the throw to the pitcher and the pitcher to the catcher who tossed it to the back stop.
If any fielder misses the ball, or errors the ball remains on the field where it is missed, i.e. the short stop lets one past her or it shoots threw her wickets. If it was clearly a field-able ball then that ball stays on the field where it come to rest.
You need to make sure you have at least 15 balls to make sure you get every player a chance to field including the catcher. Working all the way around the horn. The cleanly fielded balls always get thrown to the pitcher and then the catcher.
If the pitcher missed a ball being thrown by a fielder the ball must stay on the field. The play is over after the pitcher catches the ball. If the catcher misses a throw not intended to be a play at the plate it is not counted as a missed ball. On a play at the plate the catcher must return the ball cleanly to the pitcher to stop play. The pitcher then returns the ball to the catcher.
When the bucket is empty count the number of balls at the back stop. If you have more at the back stop than in the field stop the drill. I always like to end on a high note.