Parent.component.html

<fieldset>
  <legend>
    <h1>Parent Component</h1>
  </legend>

  <div *ngIf="brotherMessage$ | async as brotherMessage">
    <p>Son said: {{ brotherMessage }}</p>
  </div>
  <div *ngIf="sisterMessage$ | async as sisterMessage">
    <p>Daughter said: {{ sisterMessage }}</p>
  </div>

  <app-brother></app-brother>
  <app-sister></app-sister>
</fieldset>