title: how to trigger a validation of child component from parent component OnSubmit Angular 4?
body: <p>I Have forms like this, in parent i am including multiple child components each child component is formgroup. now i need to check all this child forms validation on parent form when user click OnSubmit.</p>
  
  <p>How should i trigger child form validations from parent on submit. I have used FormBuilder in each childcomponent.</p>
  
  <p>I am able to do validation when user click on child fields but if user doesn't enter anything or touched anything and try to submit validations not showing errors.</p>
  
  <p><strong>parent.component.html</strong> </p>
  
  <pre><code>&lt;form&gt;
      &lt;child1&gt;&lt;/child1&gt;
      &lt;child2&gt;&lt;/child2&gt;
      &lt;child3&gt;&lt;/child4&gt;
      &lt;child4&gt;&lt;/child4&gt;
  ''''
  ''''
  ''''
  &lt;/form&gt;
  </code></pre>
  
  <p><strong>child1.component.html</strong> </p>
  
  <pre><code>&lt;div formgroup="child1group"&gt;
        &lt;div formarray= "child1array"&gt;
        ....
        ...
        ...
        &lt;/div&gt;
  &lt;/div
  </code></pre>
  
  <p><strong>child2.component.html</strong> </p>
  
  <pre><code>&lt;div formgroup="child2group"&gt;
        &lt;div formarray= "child2array"&gt;
        ....
        ...
        ...
        &lt;/div&gt;
  &lt;/div
  </code></pre>
  
  <p>please someone tell me how to do this validation on angular 4 ?</p>