How can I programatially restart a child in Forever?

I have two servers I want Forever to monitor. If one restarts, I need to restart the other.

serverOne.on('restart', function(){
    serverTwo.restart();
});

Nothing I have tried seems to work, even though reading the code implies it should. I have also tried:

serverTwo.restart();
serverTwo.kill(false);
serverTwo.kill(true);
serverTwo.stop();

amongst others.

I understand I might need to make serverTwo do something when it loses it's connection to serverOne, but since someone else is developing those at the moment I'm looking for a way to make this work for the time being.