Kids need fun, they can create their own structures. I think more times then not the kids would be fine without adult supervision. We even had leagues and kept stats without a single adult around. I get concerned when I see an 8 year old trying to play and act like someone 12, or a 10 year old acting like someone 16. When a child misses out on all the normal social interaction without adults that takes place at this age, they often become dysfunctional adults.
Life gets serious enough fast enough.
Show them a few things to work on, but for heavens sakes don't set up drills. It is a game at this age. When you take the fun out of the game, it is no longer a game. If they want to keep scores, or compete against each other, they won't need an adult to figure that out. Let the kids grow and learn skills and sports by choice.