While practicing with my three girls at home I found it fun to pitch them tennis balls. You can pitch them very hard, they don't hurt if the batter gets hit, and a solid contact really jumps off the bat.
Tennis balls are excellent aids for kids who develop a fear of the ball.
I pitch tennis balls to them and about every third or fourth pitch, throw at them. Because they don't fear the tennis ball so much, they stay in better, and also don't seem to have any problem avoiding the ones that come at them. It's a confidence builder. A couple of our fields have home run fences set up well inside the regular fences. Even the timid kids, with a close and reachable target, light up.