Set the field up with a defined dribbling area. At one end or corner of the field you'll also need to set up a small square of discs or cones about 10 feet square. This area is the "Hospital".
Introduce the game asking if your players know what germs are and what they do. The likely answer you'll get is "they make you sick". Then, ask who we sometimes have to go see when we get sick, the answer we're looking for of course being the "Doctor".
In this game, players will dribble around with their own ball. One of the players, without a ball, will start off as a "Germ". The germ chases the players as they dribble around, and tries to tag them. If a player gets tagged, they have to dribble to the "Hospital" to see the doctor. Once at the hospital, the player does a small challenge (five knee juggles, 5 sit-ups, etc.), and then re-enters the game.
For variety, add a second, third germ, etc. For older kids, instead of tagging the players have the germ steal the ball away. Encourage your players to practice different moves as they dribble around.