Here are a couple of great drills designed to maximize your player's skill at heading the ball.
Head it! - Passing & Ball Striking
Set up a small circle of cones with you in the middle. Place all of the balls in the middle with you and set the kids up on the outside of the cones. One at a time, toss the balls to the kids and have them attempt to head them back to you. Keep instructions very simple.
Try to get them to hit the ball with the upper part of their forehead and not the top of their head. To make it more challenging you can call out "Head it" or "Catch it" and they must do the opposite of whatever you say. Each time the kids get it right, they get a point as a group. You get a point for each mistake. See who wins!
Number of Players: All
Equipment: Each child needs a ball. Enough cones for a small circle.
Heads Up - Heading
Set up several goals with cones. Place a goalkeeper in each goal. The remaining players will be paired up in groups of 2. Player 1 will toss the ball to Player 2 who will attempt to head the ball into the goal. Once the ball goes through, both players run to the other side and switch roles. Be sure to rotate your keepers so that everybody gets a chance in goal.
Number of Players: All
Equipment: Cones for goals. 1 ball per heading pair