How do I get rid of Java child processes when my Java app exits/crashes?

final String[] cmd = {"<childProcessName>"};
Process process = Runtime.getRuntime().exec(cmd);

final String[] cmd = {"<childProcessName>"};
final Process process = Runtime.getRuntime().exec(cmd);
Runnable runnable = new Runnable() {
    public void run() {
        process.destroy();
    }
};
Runtime.getRuntime().addShutdownHook(new Thread(runnable));

killall <childProcessName>