One problem we constantly have is the girls throwing "rainbows" to first base or just not having accurate throws. One drill I did was to set up a bucket (or some other target) at about what would be chest height for the average 10U player (so maybe 3.5 to 4 feet) and have them take grounders and come up throwing in an attempt to knock the bucket off. A rainbow throw won't have the oomph to knock it off even if it hits it, so they have to concentrate on making a good hard throw. I had them take the grounders from all over the infield for that. Following that drill, I set up a parent with a glove at first base and ran the same drill. They were making some great throws to first at that point. They had fun with it, too.
Don't under-value fly balls and pop-ups either. A lot of 10U players will see a pop-up, wait for it to hit the ground then pick it up and try to throw the girl out at first (even though by the time the ball came down, the girl was returning to first having already run through it).
I'm going to have to check out that website as well. Thanks