Again, I have them keep count and record in the book. Until they are confident, I usually play my outfielders deep and let the ball drop in front of them. I also use lare plastic buckets and trashcans as targets in the field, having them simulate throws to second base or home. Throwing seems so basic to us, but is so hard for these kids to understand the correct mechanics. I know it's not totally correct, but it's the only thing they understand about keeping the arm up.
Kids do like hitting most of all, but they all want to be the first hitter.
I have learned that they have to earn BP by trying the other drills. They don't have to succeed, just try. I wish I had access to a machine like you, as I am the world's worst pitcher. Trying to keep those collecting hit balls is the chore. To combat this, I try to use games that emphasize defense as well as offense.