title: Updating child's state from parent component
body: <p>Let's say that my parent component got two child component : </p>
  
  <pre><code>Parent
  | Child1
  | Child2
  </code></pre>
  
  <p>I'am getting an input from Child2 and I'am passing it to the Parent component (until now, I know how to do). But then I need to pass that input to Child1 to update it's state.</p>
  
  <p>How can I do that?</p>