How do you keep a child from suffering harm if baseball hits breastbone hard?

Breastplate: It is truly rare but I have read of kids suffering cardiac arrest when hit square in the breastbone by a line drive. The condition itself is unpredictable, ie. Who would be susceptible is unknown. I've also heard suggestions that a breastplate worn by pitchers would spread the force over a larger area and cushion the blow(&prevent it). I am not aware of any area that has tried it or results.