title: How to send a signal to a child's child after receive a signal from parent
body: <p>Background:
  I am child (A)</p>
  
  <pre><code>Original Code:
  Parent-&gt; fork [hv A PID only]
  ------------1st Child(A)-&gt; fork twice [hv Aa PID and Ab PID]
  --------------------&gt;1st Child's Child(Aa) + 2nd Child's Child(Ab)
  </code></pre>
  
  <p>This time, I would like to send a signal SIGCONT to child's children (Aa+Ab) after receive a signal SIGCONT from parent. What should I do?</p>