I’ve come up with a pretty cool and really fun hitting drill for the kids.   It goes along the same theme as your tee drill hitting square targets on a fence.   Then you can give the wooden plank a try.   It goes right along with this Beach Ball Hitting Drill.

Beach Ball Hitting Drill
Depending on the kids ability will determine how far to put the second tee in front of the main tee.
Take a second tee and place it a few feet in front of the main tee at home plate.
Set a beach ball or something similar on that second tee.
Kids have a great time trying to hit line drives to knock the beach ball off the tee.   You can move the tee around–further out or in.

Kids just love trying to knock beach ball off and at the same time it’s teaching them to concentrate driving the center of the baseball instead of dropping down to hit pop-ups.

Wooden Plank
There is another hitting drill that I use and it is pretty affective on stepping out. I made a wooden plank that sits off the ground 6 inches and the batter stands on it, so if he pulls out his front leg he will no hit because he falls off the plank.