Are they acting out at practice or games?
If practice, split the squad up into many small groups and roll through a number of skill drills, not just BP and Infield. Keep them busy. Ask the Moms and Dads to help, even the divorced ones
Boredom is the enemy of baseball practice at their age.
This is a good link:
How To Run An Efficient Baseball Practice
It is funny how times change. When I was a kid if I had acted out to the Coach I was one phone call away from Unpleasantville, My House, USA.