app.component.html
----------------------
<button class='btn' (click)="showbtnContent('btn1');">btn1</btn>
<button class='btn' (click)="showbtnContent('btn2');">btn2</btn>
<app-child></app-child>

app.component.ts
-------------------
showbtnContent(btn){
if(btn === 'btn1'){
thisbtnContent = true;
}else{
 thisbtnContent = false;

}
}
child.component.html
-------------------
<div *ngIf='thisbtnContent' id='btn1Content'>jjjjjjjjjjjjjjjjjj</div>
<div *ngIf='!thisbtnContent id='btn2Content'>jjjjjjjjjjjjjjjjjj</div>

child.component.ts
------------------------
@Component({
  selector: 'app-child'
});
thisbtnContent = true;