You might have another coach throw the kids who aren't doing the team drill some ground balls or pop ups while they are waiting. My teams used the soft baseballs in case we missed and got hit in the head. :-)
Get 2-3 T's, a couple soft toss stations, a hit'n stick, etc going all at once. Set up one station per panel of backstop--both inside and outside of the stop. Like Jack says, run as many stations as you have adults to run. Shoot for no more than 2 kids per station.
Make some or all of these stations competitions--most balls hit in a row, farthest hit, etc. Set a marker on the farthest ball hit. If you have a ton of extra parents, have one pace off and record each kid's record to try to break at the next practice.
Another non-hitting standby is a game called Guts. Set up two pairs of cone goals a few paces from each other. Two kids (one per goal) take turns rolling grounders and trying to score on the other. Balls have to be on the ground and the goals need to be spaced apart and far enough from each other to provide a challenge, but keep them safe. Kids can do this all day with very little supervision and there is a ton of motivation to stop the other's attempt to score.
Another option to this is to set up two cone squares several yards apart. Each grid is guarded by one player. Kids take turns trying to throw pop flies into the opponents grid to score. Great game to encourage circus dives!
Without at doubt, breaking them into groups and rotating them works great. Your practice time can only go a hour max and you have to be ready to stay busy throughout. Any down time in between you will lose them right away. I also notice the kids all love to do any base running drills especially when turned competitive. But all good stuff on this post.