Why would you tell only a couple JV to stay around and the other JV is optional? Then... get mad at a kid who A. just had his game canceled, and B. Just been told that his stay is optional, then he left (while a few of his team mates were told to definitely stay with V)? These kids are quick to read the writings on the wall. Here is my suggestion, talk with HC and come up with a plan for ALL things you mentioned-- Team meeting on foul ball duty (which we have kids rotate each inning so no one feels like a glorified ball shagger. They are already on the bench and now they have just been told, after game started, they have to run all over the parking lot.) How to put a helmet on and be eyes for pitchers warming up. Who is expected to clean up, drag, etc. after home games. What is the backup plan after games/practices get canceled? ALL these things must be expressed in meetings to teams. If not, they realize VERY quickly that "coach" is not on top of everything. Trust factors may start to deteriorate. I print out and post pre/post practice and game duties of each kid. Tape it to the dugout wall.
That is actually a very good idea for the foul ball duty. We have our DH do the outfield warm-up between innings and re-distribute the warm-up balls after our defensive half inning.
The reason we did the optional for some is because the area we have to work with inside is very small. If we have all of the kids from both teams in there we quickly run out of functional room and end up with a lot of standing around. The standing around part is also on the coaching staff as we need to figure out what we can do to keep them active in our small area. It is also on the players, because if we don't tell them EXACTLY what they need to be/should be doing, some of them will do nothing.
It should also be noted that he was the only one of the optional guys that did not stay.