Facing a faster pitcher than the kids normally see is a tough one. BP is for working on the swing so grooved pitches are the way to go but the kids do need to take some swings at the faster speed to get there timing down and a few games a season might not be enough. A pitching machine is good for this. So far this year my 9-10 team has face two pitchers that could really bring it. The first one had great control and if he missed it was only by inches. So I kept telling my kids dont worry about balls and strikes because they are all going to be strikes just get up there and swing at the first three. By the third time through the order they were hammering him. Of coarse all he had to do was throw it 3 feet out side and they would have all struck out hahaha. The second was wild as crap and I told my kids don't worry about hitting just try not to get killed. They pulled him after he hit 4 and walked 6.
As for 2 strikes. I don't change anything and only give one instruction. If you can touch the ball with your bat the swing at it. Most of our hits have come with two strikes because they spend less time thinking if its a ball or strike and more time just trying to hit the ball.
Bad Habits: If you aren't correcting them your coaching them.