If you have fun, they will have fun. Tease them...and then tease them some more.
(A) The team imitates you. If you walk, they walk. If you don't pay attention to them, they won't pay attention to you. If you run, they run. If you patent attention to them, they will pay attention to you.
(B) Talking is OK. Think of a beehive...there is a lot of work being done at a beehive, but it isn't particularly quiet. You should be able to hear a low buzz when the kids are working, learning and having a good time. You should have a signal for them to stop talking and listen. If they continue talking after the "be quiet" signal, they do a lap. It only takes about two laps to get the idea across.
(C) An inside joke: Have you seen the coach with his players in their position and the coach is hitting one ball at a time to each player? The good coaches see that their and laugh their a**es off.
(D) You need about a hundred softballs. You can't have too many.
(E) Keep the kids moving. Watch this video. The pace that Candrea is working the players is the same pace as you can use with your team. It isn't too fast for 12 YOA girls. Lots and lots of reps...keep them hustling.
When you teach them something, do it within the drill. E.g., if a kid doesn't field correctly *STOP* right then, tell the team to be quiet and watch, fix it, and then get right back into the drill.
The drill after this is the pop-up drill. The player takes position between 1st and 2B. You toss one right to them, then one to their right, one to their left, one where they have to run in about 15 feet, and followed by one long back to their original position. You don't stop if they miss a pop-up.
(F) Hitting is a problem...so, do station work. Soft toss at one station, tee work at another, followed by live hitting. Perhaps 3 kids at each station.
(G) End the practice with a game of some kind.
(H) If you aren't tired at the end of the practice, then you aren't working hard enough.