I think the easiet what you can do is as below, have one property bind to child and update that property on click event.
@Component({
selector: 'my-app',
template: `Welcome Parent <br>
<p>Name: <input type="text" [(ngModel)]="name" > <br></p>
<p>Mobile: <input type="text" ><br></p>
<button (click)="updatechild()">Submit</button>
<preview [param1]="forChild" ></preview>
<button (click)="add.next(control.value)">Add</button>
`
})
export class AppComponent {
public name:string="";
forChild:string="";
updatechild(){
this.forChild=this.name
}
}